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MAKING AN EXPERIMENTAL DYNAMO IN THE BOY S WORKSHOP 



^ II u^=nrc 



HARPER'S 

BEGINNING 

ELECTRICITY 



BY 

DON. CAMERON SHAFER 

'.S 



FULLY ILLUSTRATED 




! 

' HARPER & BROTHERS PUBLISHERS 

NEW YORK AND LONDON 
MCMXII 

I I n f^ir i jiiai H I □ 






COPYRIGHT. 1913. BY HARPER a BROTHERS 



PRINTED IN THE UNITED STATES OF AMERICA 
PUBLISHED OCTOBER. 1913 



//,^ 



©CLA357472 



CONTENTS 

CHAP. PAGE 

FOREWORD vii 

I. WHAT WE HAVE LEARNED ABOUT ELECTRICITY i 

Electricity is invisible, but we really know a great deal about 
it — Light, heat, and electricity are all forms of energy — Elec- 
tricity everywhere. 

II. THE BEHAVIOR OF ELECTRICAL ENERGY ... 7 

Electrical circuits are similar to water circuits — How the 
energy of the sun, stored in coal, can be changed into electricity 
and thence back into heat energy — The effect of electricity on 
the human body — Conductors, non-conductors, and condensers. 

III. STATIC OR FRICTIONAL ELECTRICITY ..... 14 

Familiar forms of static electricity and its explanation — Rela- 
tion between static sparks and lightning-discharges — ^The static 
spark and how it is produced — How static electricity accu- 
mulates on non-conductors. 

IV. SIMPLE EXPERIMENTS WITH STATIC ELECTRICITY 20 

Static electricity is produced by friction — Attraction and 
repulsion — Instruments for detecting static electricity — The 
two phases of the static charge. 

V. STATIC ELECTRICAL GENERATORS . 35 

Volta's electrophorus and how to make it — Details of other 
and more powerful static machines — Care and operation of 
static generators. 

iii 



CONTENTS 

CHAP. PAGE 

VI. EXPERIMENTS WITH THE STATIC MACHINE . . 46 

Analyzing the static spark — Care necessary in handling 
high-pressure currents — Experiments with the static spark — 
Condensers and accumulators — The Leyden jar. 

VII. FURTHER EXPERIMENTS WITH STATIC ELEC- 

TRICITY 58 

Generators and motors — Making small magnets with static 
electricity — Transmitting the current — Heating and fusing 
metals with the aid of static electricity — Electrical toys, 
Geissler tubes, and electric chimes. 

VIII. GALVANIC ELECTRICITY (,1 

Generating electricity by chemical action — Explaining the 
galvanic battery — A comparison with static electricity. 

IX. BATTERIES AND HOW TO MAKE THEM .... 74 

Volta's electric pile — Experimental zinc and copper bat- 
teries — Instruments for detecting and measuring electric 
currents — Connecting batteries in series and multiple. 

X. EXPERIMENTS WITH BATTERY CURRENTS . . 87 

The battery circuit — Splicing and tapping wires — The 
galvanoscope — Studying flow and resistance. 

XL THE ELECTRIC CIRCUIT 96 

Electricity must always flow over a circuitous path — Ex- j 

plaining the short circuit — The series and multiple circuits and ^ 

their various combinations — The metallic and ground return I 

circuits. 

XII. MAGNETISM 106 

From the lodestone to the electromagnet — The simple theory 
of magnetism — The earth as a magnet — Magnetic influence. 

XIIL THE LINES OF MAGNETIC FORCE 114 

The field of force about a magnet — The attraction and re- 
pulsion of magnets — Natural, permanent, and electromagnets 
■ — What we know about magnets. 

iv 



CONTENTS 

CHAP. PAGE 

XIV. METHODS OF MAKING PERMANENT AND ELEC- 

TROMAGNETS I20 

Several metals besides iron and steel can be magnetized 
— Making bar and horseshoe magnets — Magnetizing coils 
— Principle of the electromagnet — The helix and solenoid. 

XV. THE INDUCTION-COIL 131 

The principle of the induction-coil — Details and diagrams 
for building an induction-coil — Vibrator and condenser — 
— Experiments with induced currents. 

XVI. THE TELEGRAPH 143 

Development of the telegraph — A simple telegraph line 
— Constructing telegraph instruments and erecting circuits 
— ^The Morse code — Details of telegraph work. 

XVII. THE TELEPHONE 155 

How the voice is transmitted — ^The first successful tele- 
phone — The simplest form of electrical telephone — How to 
set up instruments and establish circuit. 

XVIII. DYNAMIC ELECTRICITY 165 

Electricity generated by mechanical power — Its relation 
to static and galvanic electricity — The dynamo, or generator 
— Its history and development — Explanation of the prin- 
ciple of the dynamo — Alternating and direct current. 

XIX. THE DYNAMO, OR GENERATOR 174 

The first dynamo and its subsequent development — 
How the dynamo produces a flow of electricity — Descrip- 
tion and working-plans for making a small dynamo — The 
transmission of dynamic electricity. 

XX. THE ELECTRIC MOTOR 189 

Changing electrical energy into mechanical energy — 
Why the motor whirls — ^Toy electric motors of various 
types — A dynamo is also a motor — Kinds and types of 
power motors. 

V 



CONTENTS 

CHAP. PA(S 

XXL CHANGING ELECTRICAL ENERGY INTO HEAT 199 
Electric heat is the product of resistance — The theon.- of 
heat — The electric flatiron and its heating-unit — Cooking 
by electricity — Measuring the heat of electricity. 

XXH. ELECTRICITY AXD LIGHT 210 

The first electric light — A comparison of various sources 
of illumination — Theon,- of light — Light-rays and color 

values — Incandescent and arc lamps — Connecting minia- 
ture lamps in electrical circuits. 

XXIII. WHAT THE BEGINNER SHOULD KNOW ABOUT 
THE ELECTRICAL EQUIPMENT OF AN AU- 
TOMOBILE 227 

The ignition system of a gasolene-engine — Electric lamps 
for the automobile — The magneto or generator — How the 
car should be wired — Self-starters — ^The storage battery. 



APPENDIX— A LITTLE HISTORY OF ELECTRICITY^ . . 239 
The discover^' of the magnet — Electric fish — First static 
experiments — The first book about electricity — Early 
t^-pes of static electric machines — Accidental discover}' 
of the Leyden jar — The discover}' of induced currents — 
The birth of the batten.' — Volta makes first wet batter}' — 
The first electric arc — \^ hen the electromagnet was new — 
Ohm works out laws of electricit}' — The first successful 
electric motor — Discovery of the djTiamo — Morse pro- 
duces the telegraph — Perfecting the dynamo, or generator — 
— The first arc-lamps — ^The search for the incandescent 
lamp — World's first electric-light station — The beginning 
of the telephone — Transmitting the new energy. 

THE ELECTRICAL DICTIONARY 267 

Electrical terms explained. 

INDEX 275 



FOREWORD 

ELECTRICITY is as old as the stars. But only recent- 
ly has it been doing a thousand and one tasks in home 
iand office, factory and mill, mine and railroad — tasks which 
are as nothing to its giant strength. 

Il The wonder-workings accredited to the fabled genii of 
j childhood lore are insignificant compared with the marvels 
which electricity has wrought. A flash, and our messages 
cross the seas. With the speed of light our voices span 
the continent. Silently, invisibly, electricity hauls the 
heaviest trains, accomplishes the hardest tasks. At the 
pressure of a finger it lights and heats the home. In shop 
and mill it does more work than all the laborers of the 
world. 

Every one should know something about this mighty 
energy which blazes into light at the touch of a button, which 
exerts the strength of giants when a switch is thrown, which 
faithfully performs the drudgery of home and factory, hesi- 
tating at no taskj however menial, however laborious. 

This book explains electricity very simply in connection 
with experiments which any boy can do and devices which 
any boy can make. This introduction to electricity has 
been written with the feeling that electricity is a friend and 
playmate with whom we can easily become intimate. Ob- 
viously, the best way to learn about electricity is to do 
something with it in addition to reading about it. This 
adds personal interest and entertainment to the acquisition 

vii 



FOREWORD 

of a knowledge which will open up a new world to the be- 
ginner and give him a better acquaintance with the electri- 
cal wonders of to-day. 

Children are taught to keep away from deep water and 
high cliffs; they are instructed to be careful of machinery 
of all kinds, of sharp knives and firearms. They should 
also be taught to respect electricity. Care and prudence 
are necessary in dealing with all electrical apparatus. 1^' 
Wherever electricity is carried over long distances, from a 
water-power station to a cit}" or from village to village, it 
is under high pressure, and must be left severely alone. 
These power-wires are always suspended high in the air, 
but it is dangerous to touch them even accidentally with a 
fish-pole. If such a line sags low or is accidentally broken, 
keep away from it. 

The wiring about the house should not be tampered with. 
Houses are wired by competent electricians who take every 
precaution to guard against any leakage of current — any i' 
places where the electricity can leave the wires and cause 
trouble. This wiring is always finally inspected by the in- 
surance authorities, and should be left just as it is installed. 
The current used for house-lighting is not considered dan- 
gerous. There is more danger from serious burns and fires 
than from "shock," as a result of tampering with the electric- 
light wires. 

Whenever there is new wiring to install, lines to be ex- 
tended, changes to be made, the work should be trusted to 
a man experienced in electrical matters. 

Leyden jars are used to store up the electricity produced 
b}^ the static machines. These jars will hold only a little 
electricity, but it is under enormous pressure. The dis- 
charge from a small jar is ver}' unpleasant. The discharge 
from two or more jars should be carefully avoided. Care 

viii 



FOREWORD 

should also be taken in handling large induction-coils. 
Never play practical jokes with electricity. 

But there are thousands of simple and harmless experi- 
ments with electric batteries, motors, static machines, etc., 
I which cannot fail to interest every one. Electricity is one 
I of the most absorbing of all our studies. It stimulates the 
! imagination, exercises all the faculties, and develops the 
I mind. Batteries, friction-machines, and toy dynamos are 
j innocent of any harm. Associating electricity with light- 
j ning has instilled fear in the hearts of many. Electricity is 
not to be dreaded, not to be feared. A little education 
always removes this element of fear. 

The author has found by experience that much which is 
written for younger readers is not sufficiently direct or con- 
venient in its application. Living as the author does in a 
great electrical center, surrounded by the manifold applica- 
tions of this tremendous power, he is fully aware of its 
complexity in use. But he also knows the necessity of 
introduction — of a beginning, and Beginning Electricity has 
been planned most carefully to avoid the difficulties often 
met with in books, and to offer a helping hand to the real 
beginner. 

Don. Cameron Shafer. 

Schenectady, New York, June i, 1913. 



1^ 



HARPER'S BEGINNING ELECTRICITY 



HARPER^S 

'beginning electricity 

Chapter I 

I WHAT WE HAVE LEARNED ABOUT ELECTRICITY 

THERE are, generally speaking, three ways of produc- 
ing an electric current, all very closely related. 

Electricity can be produced by rubbing, or friction. This 
is static, or stationary, electricity. 

Electricity can be produced by the action of chemicals. 
This is known as galvanic electricity, after the Italian 
scientist Galvani, its discoverer. 

Electricity can be secured from magnets. This is termed 
dynamic electricity. The machine which produces it is 
called a dynamo. 

Electricity can also be produced by heat, a process called 
thermo-electric generation, but not in quantities large 
enough to be seriously considered. 

We really know a great deal about electricity. 

Because electricity is invisible and so very new and 
strange to most of us is no reason to speak of it in awed 
whispers. It should not be classified with the mysterious 
and unknowable. Electricity is a wonderful form of 

I 



HARPER'S BEGINNING ELECTRICITY 

energy. We actually know just as much about it, if not 
more, than we know about steam. 

Steam itself is quite as invisible as electricity. That 
which we see issuing from the tea-kettle spout is not steam, 
but water-vapor. It is steam being condensed back into 
water by contact with the cold air. The steam near the 
hot spout is quite invisible About an inch from the spout 
it begins to cool. As it cools it condenses into tiny particles 
of water. It is these minute drops of water that we see and 
miscall steam. Steam flowing through a hot glass tube 
cannot be seen any more than we can see electricity flowing I 
over a copper wire. But we are familiar with steam. We f 
have known it a long, long time, and intimacy has de- 
stroyed the mystery of this form of energy. 

Steam is a hot gas capable of great expansion, from which 
we get mechanical energ3^ This is all we know about 'i 
steam, although we do know how it behaves under certain f 
limited conditions. 

4 

Some Things that We Know 

When we become familiar with electricity, through study 
and appHcation, it quickly loses its mystery. We are hap- 
pily surprised to find that we actually know and under- f 
stand a great deal about this form of energy. 

Electricity is a form of energy — and that is all we really f 
know about it. But we have learned to measure this electric 
force with the greatest accuracy. We have discovered the 
laws which govern its behavior under various conditions. 

Electricity is much like the force called gravitation. We 
understand this law of gravitation, that a stone cast from 
a height will always fall directly toward the center of the 
earth at a certain increasing speed. The falHng stone is 

2 



t 



ABOUT ELECTRICITY 

propelled by a wonderful invisible force called gravitation; 
but we do not know just what constitutes gravity. 

Gravity attracts all things, whether magnetic or not. 

Seemingly, it must always travel with a falling body. 

! Electricity does not attract all things. Indeed, it repels 

I quite as often as it attracts. It not only travels with a 

body, but through it. The strange force called cohesion 

I exists only in material itself. It cannot travel from one 

body to another. Its office is to hold all material together. 

Heat must always flow from one body to another. It 

i cannot be stored up. Electricity travels freely from one 

I body to another, and yet it is not heat. 

, Electricity travels with the same speed as light. Light 
and electricity have no weight, and, therefore, no power of 
impact It is the weight of the rifle-bullet, plus its speed, 
which gives it an enormous impact force. As light and 
electricity weigh practically nothing, they can have no per- 
ceptible impact force, even though they travel at enormous 
speed. 

Light, heat, and electricity are all various forms of energy. 
All are more or less closely related. 

Electricity will produce heat; heat will produce elec- 
tricity. Electricity produces light, and light can produce 
electricity. Mechanical energy will produce electricity, and 
electricity, in turn, will produce mechanical energy. 

The movement of electricity seems to be like that of water, 
always from a higher to a lower level. Water is equalized 
at its lowest level, which is the level of the sea. Raise it 
above this level and It will always strive to flow back. 
Electricity seems to have a neutral point. Raise It above 
this level and it will flow back at every opportunity. 

It is true that electricity cannot be seen, and yet It gives 
the most powerful artificial light in the world. It is noise- 

3 



HARPER'S BEGINNING ELECTRICITY 

less, and yet it causes the mighty peals of thunder and 
faithfully reproduces the faintest whisper in the telephone. 
It has no weight, and yet it whirls the largest machinery 
and hauls the heaviest trains. We cannot see it or weigh 
it, but we can measure it with the greatest accuracy. We 
know how fast it travels; we can gage its pressure, its 
working-energy, the quantity flowing over a wire, or the 
amount of light, heat, or motive power it will give. The 
laws which govern its every movement are well known, but y 
we do not know much about the exact nature of electricity. ' 

Electricity may be a form of wave-motion, like heat and 
light and sound. We know that as soon as the molecules 
in a piece of iron are violently agitated by hammering the ' 
iron begins to get hot (a molecule is the smallest particle of 
any material). If the hammering is continued the iron will 
finally get red-hot. As soon as the iron is hot enough it 
begins to give out rays of light. As the agitation of the . 
molecules increases, the brilliancy of the light increases. 
From red the light turns orange, and from orange to yellow, 
and finally to a brilliant white light. This heat, and con- 
sequent light, can also be produced by the application of 
electricity to the iron, which would tend to prove that 
electricity is but a wave-motion. 

That electricity has no weight seems to be proven by the 
fact that a wire weighs exactly the same after being charged 
with electricity as it did before. The finest scales show no 
difference in the weight. But a steel bar will be a little 
longer when magnetized, which shows that electricity has 
disturbed the molecules of steel in the bar. 

Whatever electricity is, for the sake of simplicity let us 
assume that it is an invisible fluid, without weight, capable 
of very rapid motion. Just how fast it travels is astonish- u 
ing. It will flow over an electrical conductor at the terrific 

4 



ABOUT ELECTRICITY 

speed of 186,165 miles a second, or at nearly the same speed as 
light. This enormous speed is not appreciated until you 
stop to think that it will circle the earth nearly eight times 
within a second. This explains why the telegraph and the 
telephone are nearl}^ instantaneous, regardless of distance. 

Electricity Everywhere 

Electricity is present on every side, in everything, in some 
quantity. The earth is a huge storehouse of electricity. 
The very air is full of it. 

Electricity flows through all substances to a certain de- 
gree. Some materials almost wholly oppose, or resist, its 
passage. Others allow it to move with the greatest free- 
dom. Electricity flows easiest through metals. It will 
flow through a silver wire as readily as water will flow 
through a pipe. It will flow through copper almost as well. 
This latter metal is used almost exclusively where good con- 
ductors of electricity are required, because silver is too ex- 
pensive. Electricity will flow through iron and steel fairly 
well, but less than one-seventh as well as copper. Elec- 
tricity does not flow readily through the air or through 
gases. There are innumerable materials which resist its 
passage, such as mica, glass, porcelain, rubber, oils, wax, 
shellac, resin, dry wood, and dry fabrics of all kinds. 

We live in a world of electricity, surrounded by it on every 
side. But we only notice it when it is in motion, or when 
the quantity present is more or less than the average amount. 
Electricity is a form of energy and, therefore, cannot be 
destroyed. It is not aff'ected by heat or cold in ordinary 
degrees. 

Electricity can be easily and quickly changed to other 
forms of energy. It can be changed to light-energy through 

5 



HARPER'S BEGINNING ELECTRICITY 

the medium of an electric lamp. It can be changed to heat- 
energy, for heating purposes, by placing resistance or 
friction in its path. It can be changed to mechanical 
energy b}^ the application of an electric motor. 

And it is in these three forms that we know electricity 
best. 

As a matter of fact, the knowledge of the exact nature of 
electricity would be of little value to us, beyond adding 
materially to our scientific discoveries, unless it showed a 
way to produce this form of energy vastly cheaper than 
present-day methods. We are interested only in the effects 
of electrical energy — what it will do — and that is all. 

What is electricity t As well ask what is gravity, cohesion, 
matter. Judging from what has been done in the develop- 
ment of electricity during the past twenty-five years, this 
question will not long remain unanswered. 



p 



Chapter II 

THE BEHAVIOR OF ELECTRICAL ENERGY 

THE path over which electricity moves is called a 
circuit. 
This is because electricity always flows in a complete 
circle, just the same as water flows over a circuitous route. 
This does not mean that either electricity or water must 
always travel in a geometrical circle. It is called an electric 
circuit only because a path must be provided for its return, 
wherever it is carried, or it will cease to flow. This is 
equally true of water. The sun raises water from the sea 
by evaporation. It falls to the mountains in the form of 
rain. The path must be open for its return to the sea again, 
or it will cease to flow. 



WtR,E 



PUSH BUTTON ELECTRIC BELL 



BATTERY 



Ftff.t 



Electricity always flows in a circular path along the vari- 
ous wires (Fig. i). Always it must return to its source. 
Break or cut the wire at any. point and the flow ceases 
instantly. This is because a break in the circuit is actually 

7 



HARPER'S BEGINNING ELECTRICITY 

an obstruction in its path. It cannot travel through the 
air Hke water. Water can be raised from a reservoir with 
a pump and pushed through a long pipe. As long as this 
pipe is not obstructed the water will flow back into the 
reservoir again. Close the pipe at any point and the flow 
will cease instantly (Fig. 2). 



^ 



PUMP 



^ 



> 



Fig. 2 



% 



RESERVOIR 



Electrical circuits vary in form and extent, but this prin- 
ciple of a continuous path ever remains the same. No 
matter where electricity is carried over a wire about the 
house or factory, another wire must be provided for its re- 
turn to its source or it cannot flow. 

Electricity is indestructible. It cannot be used up or 
destroyed. It is a mistake to think that electricity is con- 
sumed and burned up in the electric-hght bulb like kerosene 
in an oil-lamp. Electricity is not burned and consumed in 
an electric range like coal in a kitchen stove. The elec- 
tricity which returns to its original source after its work is 
done is no diff'erent than it was when it left. It is the 
working-energy of electricity which is consumed, just as it j 
is the energy of falling water which is utilized to turn a 
water-wheel, and not the water itself. Just as much water 
escapes from the tailrace of a water-power plant as enters 
the head-gates. Just as much electricity flows back to a 
battery or dynamo as started over the circuit. 

It requires a certain amount of "sun-energy" to raise a 
quantity of water to a certain height. This energy is thus 

8 



ELECTRICAL ENERGY 

imparted to the water, and it will produce an equal amount 
of energy in racing back to the sea. This energy is usually 
wasted in passing over such rocks and stones as obstruct its 
path. Water without pressure or elevation has no energy 
and will do no work. We get electrical power by raising 
the pressure of electricity with mechanical power, or other- 
wise, and this pressure will perform a certain amount of 
work as the current flows back to its source. Electricity 
without pressure will do no work. 

Conductors and Non-conductors 

Water will not flow through some materials. It will flow 
through others with the greatest ease, whereas nearly every 
substance resists the flow of electricity to a greater or less 
degree. This quality is well named resistance. The resist- 
ance of some materials is greater than that of others. When 
electricity flows easily through a substance, like copper, the 
material is said to be a good conductor. This means that 
it will conduct, or carry, electricity with very little re- 
sistance. 

Materials which oppose the flow of electricity are called 
non-conductors. This means that they do not conduct. A 
conductor covered with a non-conducting substance is said 
to be insulated. The word insulate is derived from the Latin 
insula, an island. The word insulated means literally that 
the body has been isolated, cut oflF from the mainland, 
removed from electrical communication with all others. 

All metals are good conductors. The most common non- 
conductors are porcelain, glass, mica, stoneware, slate, marble, 
rubber, oils, parafl&n, shellac, dry paper, silk, cloth, etc. 

It requires considerable force to lift water from a reservoir 
and push it through a long pipe. This is because the pull 

9 



HARPER'S BEGINNING ELECTRICITY 

of gravity and the friction of the inside of the pipe must be 
overcome. This force is called pressure in hydraulics. 

It also requires force to produce motion in electricity. 
The energy required to push electricity along a wire is 
called voltage, instead of pressure, although it means about 
the same thing. 

The unit of hydraulic pressure is expressed in pounds to 
the square inch of surface affected. 

The unit of electrical energy is called the volt, in honor of 
Volta, one of the pioneer discoverers of electricity. 

In overcoming the resistance in a wire circuit, the electric 
current will lose some of its energy, and will, therefore, have 
less voltage, or pressure, the farther it travels. This differ- 
ence in voltage in an electrical circuit corresponds to the loss [ 





'' 


->i 


A 

I 4- 




— ^ 




— f/o/ 


^ 




B 


J^&^} 










^h h 


-^^/ 




< 

Fig. 3 






i. 

QENE 


RATOR 





of pressure in a water pipe, which diminishes rapidl}^ as the 
pipe is extended from the pump (Fig. 3). To overcome 
some of the resistance of the wire between A and B the 
electricity will lose some of its energy. Therefore it will 
show less pressure at B than at A. 

Voltage, or pressure, is sometimes called potential. This 
word is taken from the Latin potentia, meaning power. 

When a wire is carrying a current of electricit}^ it is said 
to be charged. Electricians also speak of wires as being alive\ 
and dead. Wires are alive only when carr3ang a current. 

10 



ELECTRICAL ENERGY 

When a strong current of electricity is sent through the 
human body it makes the muscles tingle and causes them 
to contract violently. This sudden contraction of the mus- 
cular tissues has led to the adoption of the word shock. 
When we read that any one has received a shock of elec- 
tricity it means that they have in some manner interposed 
a part of their body into an electrical circuit, allowing a 
portion of the current to travel through the muscles. Only 
shocks from very high voltage, or potential, are dangerous. 
The body offers so much natural resistance to the flow of 
electricity that low voltages, such as are commonly em- 
ployed for house-lighting, etc., are not considered dangerous. 

We may not know exactly what electricity is, but we do 
know that it is a form of energy. Right here it may be ^ell 
to explain this natural phenomena we speak of as energy. 

Forms of Energy 

A person is said to be energetic, to have lots of energy, 
when he accomplishes a great deal of work. The word 
" energy " really means a capacity for doing work. When a 
man walks, when a wheel turns, when a stone is lifted, energy 
must be expended. And energy, like money, must first be 
acquired before it can be expended. It is a common belief 
that energy, once expended, is gone forever. This is far 
from being true. Energy is never annihilated, never passes 
out of existence. Energy is quick to change its form, how- 
ever. It disappears only to reappear in some other shape. 

It is easy to show that energy can be made to change its 
form a great many times. Imagine a steam-pump busy 
filling a large tank with water. First the energy of the sun- 
shine is stored up in the coal which is being fed to the 
boilers. This energy of the coal, released by the fire, is 

II 



HARPER'S BEGINNING ELECTRICITY 

quickly changed to heat-energy and then to steam-energy. 
The steam-energy is, in turn, converted to mechanical energy 
through the medium of the steam-engine. This mechanical 
energy, acting on the pump, raises the water to the reservoir. 
After all these changes we now have the original energy of 
the coal, minus some loss, represented by a quantity of 
water elevated to a certain height above sea-level. 

As long as the water remains in the reservoir it will do no 
work. The instant the water is released the energy im- 
mediately reappears, and may be made to turn a water- 
wheel. We can belt the water-wheel to an electric dynamo 
and change the mechanical energy into electrical energy. 
If we wish we can change this electrical energy back into 
heat or light energy. By placing a motor in circuit with the 
dynamo we can change it back to mechanical energy. 

It is even possible for us to belt the electric motor to a 
pump and raise some of the water back to the reservoir. 
On the face of it this looks as though the great problem of 
perpetual motion had been solved — but it has not. There 
are a great many losses every time the form of energy is 
changed. The energy itself is not lost — it is wasted. It 
is changed into heat in overcoming friction, and otherwise 
leaks away. Only a small percentage of the original coal- 
energy is left in the form of electrical energy. The energy 
which is lost during these transformations is dissipated, and 
becomes non-available to man. 

The amount of energv, or power, to be obtained from a 
current of electricity depends upon the quantit}' and its 
pressure. It is comparable to water in this respect. In 
considering the power to be obtained from a stream of water 
we must know the size of the stream and its head, or the 
height of its fall, which determine the pressure. The energy 
of a stream of water is always in exact proportion to its fall. 

12 



ELECTRICAL ENERGY 

A rather large stream, with a fall of but a few feet, will 
produce a hundred horse-power of energy. A vastly smaller 
stream, with a hundred-foot fall, will produce an equal 
amount of working-energy. 

In determining the energy of electricity we must always 
consider the size of the current and its force. Power- 
companies fix their charges on the amount of current and 
the pressure. They cannot fix it upon the quantity con- 
sumed, as they do gas and kerosene, because no electricity 
is consumed. It returns to the power-house, after its work 
is done, Hke water to the sea. 



Chapter III 

STATIC OR FRICTIONAL ELECTRICITY 

THE word static is derived from the Greek statikos, 
"causing to stand." It is used to express that pecu- 
liar characteristic of electricity which causes it to collect 
to some extent on nearly all materials. It is brought to our 
notice, usualh^, when it leaps from a charged body with a 
brilliant spark and a crackling noise. 

Static electricity seems to be ever37^where. We are quite 
surrounded b}^ it on all sides. It is in the earth, the air, 
in our clothes, on the books, the rug, and the walls. It 
collects on everything. It sticks the papers together on 
the desk. It attracts feathers and bits of lint to metal and 
glass. It leaps from our fingers when we touch "metal ob- 
jects. Now and then a crackling noise will be heard when 
the coat is being taken off. A woolen shirt or sweater 
drawn quickly over the head will produce crackling sparks. 
By scuffling the dry feet over the carpet a considerable 
spark can be secured from the fingers. 

Bear in mind that static electricity is not the kind that is 
used to light the electric lamps in the house. Very little 
work has ever been found for static electricity. It is a worth- 
less vagabond delighting in mad pranks. In the form of 
lightning it dashes down from the sk}^ scaring honest folk 
nearly to death, often doing considerable damage. It fre- 
quently visits the press-room in large printing- establish- 

H 




LIGHTNING-DISCHARGE 



LIGHTNING STRIKING BUILDING 



STATIC ELECTRICITY 

ments and sticks the sheets of paper together until the 
presses have to be stopped. It gathers on the yarns and 
threads in textile mills, knotting and tangling them, and is 
always into mischief. 

Familiar Forms of Static Electricity 

It is easy enough to prove the presence of static electricity. 
Rub a bit of amber, glass, hard rubber, or sealing-wax with 
a silk handkerchief or a piece of woolen cloth, and it will 
attract bits of paper and small particles of metal. When 
we stroke the cat's back this static electricity collects very 
rapidly. It snaps and crackles and flashes as it discharges 
between our fingers and the animal's fur. This display of 
static electricity is nothing more or less than a miniature 
thunder-shower — without the rain. 

Perhaps the most noticeable manifestation of static elec- 
tricity is Hghtning. The flash of Hghtning is but a static 
spark, such as we get from the cat's back, magnified thou- 
sands of times. 

Lightning is caused by static electricity which has ac- 
cumulated in the black thunder-clouds. These clouds are 
carrying an enormous load of static electricity, under heavy 
pressure, as well as a burden of moisture. When either 
load becomes too heavy it is dumped off on the earth. 

In plainer words, when the particles of moisture con- 
dense into large rain-drops and become too heavy to float 
in the air, we have a shower of water. When the static 
electricity becomes too condensed to remain longer in the 
air it discharges to the earth, and we have a shower of 
electricity. 

Air will not conduct electricity to any noticeable degree. 
In order to cause a static spark between two objects it is 

17 



HARPER'S BEGINNING ELECTRICITY 

necessar}^ to raise the voltage, or pressure, of the current 
until it is sufficient to "break down" this air resistance so it 
can jump across. It requires a pressure of nearly 20,000 
volts to jump across the first inch of air gap, 40,000 volts for 
a two-inch gap, 60,000 for a three-inch gap, and so on. If 
this be true, a discharge of lightning from a cloud to the 
earth, over a distance of half a mile, must represent an 
enormous pressure running well up into the millions of volts. 
A body charged with static electricity evidences some of the 
peculiarities of a magnet. It is surrounded by a "field of 
magnetic force." It attracts and repels. 

The presence of considerable heat as well as light in any 
static spark can be easily proven by the ease with which a 
small spark will light the illuminating-gas or explode a pinch 
of gunpowder. It requires heat to light the gas or to fire 
the powder. Light alone will not do this. Even the 
strongest sunshine cannot light the gas. 

The snap following the static spark is probably the 
vacuum caused by the passage of the current being closed 
by the normal air pressure, which is fifteen pounds to the 
square inch. 

Static electricity cannot collect on any material unless 
that material is a non-conductor. A good conductor can- 
not "collect" a charge of electricity, because the electricity 
readily escapes over its surface as fast as it is produced and 
flows back to the earth to maintain the universal balance. 
You can carry water in a pail, but 3'ou cannot carry it in a 
sieve. Conductors allow the free passage of electricity, just 
as the sieve allows the free passage of water. Non-con- 
ductors do not allow the passage of electricity, just as the 
pail holds the water. 

A bit of glass, rubbed with silk, evidences static electricity 
when brought near a bit of paper. When this electricity 

18 



STATIC ELECTRICITY 

accumulates on the glass it is said to be charged. When the 
electricity disappears by contact with the finger or any other 
object the rod is said to be discharged. 

If a good conductor of static electricity is insulated it will 
retain its charge quite as well as any non-conductor. If 
the sieve is inclosed in a pail it can be said to hold water. 

Static electricity spreads rapidly and evenly over the 
surface of a good conductor. On non-conductors static 
electricity cannot spread. It must remain in one place 
until it is carried off, piecemeal as it were, by the molecules 
of the air. 

It will be readily noticed that when static electricity col- 
lects on any material it extends an invisible influence out 
into the atmosphere for a considerable distance. This 
influence affects anything brought within reach of its lines 
of force. These invisible lines of force have great penetrat- 
ing powers. Magnets will attract particles of metals 
through glass and other non-conducting substances. The 
*'rays" from a bit of hard rubber, electrically excited by 
friction, readily penetrate paper, cardboard, and even glass, 
to attract or repel bits of paper and lint. 

Another wonderful manifestation of static electricity is 
the great aurora, or "northern lights," of the polar regions. 
When this phenomenon occurs in the northern or arctic 
regions it is called the aurora horealis. When it occurs in 
the southern hemisphere it is called the aurora australis. 
2 



I 



Chapter IV , 

SIMPLE EXPERIMENTS WITH STATIC ELECTRICITY M. 

STATIC electricity is all about us. It seems to be al- 
ways present. But it is noticeable only when it 
collects in more than ordinary quantities. The first hint 
of an accumulation of static electricity on any substance is 
a strange attraction for bits of paper, feathers, threads, lint, 
dust, etc. Often sheets of writing-paper will stick together ;; 
with a peculiar magnetic force. If a fur-lined coat be hastily [ 
taken off a faint crackling sound is frequently heard, and 
sometimes bright sparks are visible in the darkness of the hall. 
When static electricity accumulates on any material it 
produces an effect similar to that of a magnet. It attracts 
lighter bodies, which cling to it with remarkable tenacity. 
Any number of substances can be made to assume a mag- 
netic condition when rubbed to produce an accumulation of 
static electricity. Electricity produced in this way is sup- 
posed to be at rest, hence the name static, to stand. It is 
at rest only because it cannot get awa}^ — it is insulated, 
actually imprisoned. Given an opportunity to escape along [ 
some good conductor, and it vanishes instantl}^ and quite as 
fast as any other form of electricity. Its speed is astonish- 
ing when it does travel, being something over 186,000 miles 
a second. Because static electricity is induced by friction, ' 
which is a form of mechanical energy, it is sometimes spoken 
of as frictional electricity. 

20 



STATIC ELECTRICITY EXPERIMENTS 

For hundreds of years it was thought that amber alone 
was capable of producing static electricity. Amber being 
nothing more or less than fossilized, or petrified, resin. Dr. 
Gilbert, the English scientist, tried to electrify a cake of 
resin, and succeeded. This led him to a long series of 
experiments, during which he proved to the world that 
electricity can be generated on all substances by applying 
friction. He electrified glass, sealing-wax, shellac, sulphur, 
and a large number of other materials. He proved that the 
static electricity generated on a glass rod was held captive by 
the non-conducting glass and the surrounding air, through 
which it could not travel and thus escape back to earth. 
When a metal rod is rubbed with silk, static electricity is 
generated just the same as when the glass rod is rubbed. 
But the static current readily escapes from the metal rod. 
It flows through the rod, thence through the arm and the 
body to the earth, quite as fast as it is produced. By insulat- 
ing the metal rod with a glass handle, over which the 
electricity could not escape, Gilbert performed exactly the 
same experiments as with a rod of glass. 

Easy Experiments 

Electricity can be produced on any substance by friction. 
Drying a glass, drawing a silk ribbon rapidly through the 
fingers, sandpapering a board, polishing the stove, all pro- 
duce electrical energy. Tapping a pencil on the table pro- 
duces electricity. Chips falling from the ax are electrically 
charged. Escaping steam and the heating of metals pro- 
duce electrical disturbances. Waving a paper in the air, 
shoving a book on the table, sharpening the carving-knife, 
all produce electricity in some slight degree, although it re- 
quires a delicate instrument to detect it in most instances, 

21 



HARPER'S BEGINNING ELECTRICITY 

What boy or girl has not produced static sparks by strok- 
ing a cat's back? Large quantities of bright sparks can be 
produced in this way. It would seem as though black cats 
gave the most and the brightest sparks, but this is hardly 
probable. Perhaps the sparks are more easily seen on a 
black cat than on one of another color. 

A very simple experiment to demonstrate the presence 
of static electricity, and to show its powers of attraction at 
the same time, is accompKshed with a large sheet of common 
brown wrapping-paper. Warm the paper by the fire to dis- 
pel any dampness. Rub it briskly on one surface with a 
silk handkerchief. Place the sheet up against the wall, and 
it will stick tightly to the wall-paper for several minutes, 
or until both become charged alike. 

Balance a silver spoon on the cork of a bottle so that it 
is free to turn easily. It is best to whittle the cork to a 
point. Electrify a stick of sealing-wax by rubbing it with 
a silk handkerchief, and present it to the spoon. Instantly 
the spoon will swing toward the wax. It can be made to 
revolve very fast in its effort to come in contact with the 
electrified wax. 

Another novel experiment with static electricity is to 
take a shallow cigar-box and line it on the inside with tin- 
foil. Replace the cover with a thin pane of glass. In this 
box place any number of small figures cut out of tissue-, 
paper or dry pith. They can be painted to represent men, 
animals, butterflies, insects, etc. The figures will rest on 
the bottom of the box until the glass is rubbed briskly with 
a silk cloth, or, better still, a piece of soft leather. This 
charges the surface of the glass with electricity, and the pith 
figures will be attracted and repelled until they dance about 
in a very Hvely and lifelike manner. 

If the back of a hard-rubber comb be briskly rubbed for 



STATIC ELECTRICITY EXPERIMENTS 

a few seconds on the sleeve, or with a piece of silk, it 
will become charged with static electricity^ Present the 
charged end to a bit of feather, a small piece of tissue-paper, 
lint, thread, or even a bit of tin-foil, and these small particles 
will jump through the air and adhere to the comb for an 
instant. 

Now another strange thing becomes noticeable. The 
tiny particles of tin-foil leap to the charged comb and as 
quickly jump away from it. The bits of lint and paper only 
cling an instant, and then seem to be forcibly thrown aside. 
If this experiment is performed on an insulating glass plate, 
or a well-varnished table-top, the tiny particles will not be 
attracted again toward the charged comb. Instead they 
will leap away from it. 

Attraction and Repulsion 

With this simple experiment it is shown that electricity 
not only attracts, but repels. The fact that it first attracts and 
then repels an object leads to the conclusion that some change 
must take place in the attracted body as soon as it touches 
the electrified surface, otherwise it would not be repelled. 

Otto von Guericke, one of the first students of electricity, 
noticed this peculiarity of electrical attraction and repulsion 
more than two hundred and fifty years ago. He noted that 
a bit of feather was first attracted and then repelled by the 
electrified amber. He immediately reached the conclusion 
that the feather became electrified by contact with the 
charged amber. From this he evolved the law that all 
electrified bodies repel each other. 

This was an excellent theory, but other experiments 
proved that it was far from being perfect. The bit of 
feather behaved exactly as Guericke said it did. It was 

23 



HARPER'S BEGINNING ELECTRICITY 



first attracted to the charged amber, where it partook of the 
charge and became electrified. Then it was repelled from 
the electrified amber. But, strange to say, the bit of 
charged feather, while it was repelled by the electrified amber, 
was instantly attracted by an electrified rod of glass. Ex- 
periments showed that Guericke's law held good with many 
substances and proved entirely wrong with others. These 
experiments seemed to demonstrate that there are two 
kinds of static electricity. Assuming that there are two 
kinds of static electricity, one produced by the amber and 
another by the glass, Guericke's law could not be denied. 
All those early scientists believed in two kinds of static 

current. They designated them 
as viterous and resinous electri- 
city, and they were so called for 
a great many years. 

When the rubber comb is 
charged and the particles are 
not, they are attracted to the 
comb. When the particles, by 
contact with the charged comb, 
have each absorbed a similar 
charge of electricity, they are 
repelled by the comb. 

This experiment is best per- 
formed by suspending a tiny 
piece of dry tissue-paper from an 
insulating silk thread about a foot 
long. When the "charged comb 
is presented to the paper the 
paper is instantly attracted to the electrified rubber. It 
adheres to the surface of the rubber until it absorbs part 
of the charge. This charge cannot instantly escape from 

24 




Fig.t 



STATIC ELECTRICITY EXPERIMENTS 

the paper, owing to the insulating properties of the silk 
thread and the surrounding air. When the comb is re- 
charged the charged paper flies quickly away from it. No 
matter how the comb is held, the charged paper will always 
move away from it, for such is one of the absolute laws of 
electricity (Fig. i). 

Charge the bit of paper by contact with the electrified 
rubber until they actively repel each other. Warm a glass 
rod, or the edge of a wine glass, and charge it by rubbing it 
with the same cloth as was used to charge the comb. Present 
the glass to the charged paper and it will be attracted. 

Thus you will find, to your ever-increasing wonder, that 
the charged paper is attracted to the charged glass and 
repelled by the charged comb whenever it is first charged 
from the rubber. If it receives its initial charge from the 
glass this order will be reversed, and it will be repelled by 
the glass and attracted by the comb. 

Positive and Negative 

Benjamin FrankHn, as well as others before him, noticed 
this same thing. Franklin did not think much of the two- 
fluid theory advanced by Dufay and Guericke. He did not 
like the words viterous, for substances of the same character 
as glass, and resinous, for those substances similar to resin 
and rubber. He coined the words positive charge and 
negative charge to explain the attraction and repulsion of 
electrified bodies. 

It will be noted that when the paper is charged from the 
rubber it is repelled by the rubber — evidencing that they 
carry the same charge of electricity, which is negative. When 
the glass, charged with positive electricity, is brought near 
the electrified paper they are no longer alike, and attract 

25 



HARPER'S BEGINNING ELECTRICITY 

each other. When the paper is discharged, by contact with 
a good conductor such as iron, and recharged from the 
positive glass, it quickly repels the glass, but is attracted 
toward the negative charge on the surface of the rubber 
comb. 

In this way it is easy to understand that all electric 
charges are divided into two parts — positive, sometimes in- 
dicated by the plus ( + ) sign, and negative, indicated by the 
minus ( — ) sign. 

Charges of opposite nature always attract each other. 
This is, indeed, the first and fundamental law of electricity. 
Thus, a positively charged body attracts an uncharged body, 
or a body negatively charged. Similar charges repel each 
other. Positive repels positive, negative repels negative. 
Uncharged bodies are neutral and have no effect upon each 
other. 

This is the first lesson in electricity. To understand the 
powerful electrical machinery in a modern power-house, and 
the electrical apparatus now in general use throughout the 
world, it is necessary to learn these basic rules and principles. 

Easy Illustrations 

For these elementary experiments with bits of paper, 
pith balls, lint, or pieces of tin-foil, one can use a glass rod, 
a cake of resin, a piece of hard rubber, a roll of sulphur, or 
a stick of sealing-wax. All will become charged with static 
electricity when rubbed with silk, dry flannel, or a piece of 
soft fur. These materials will retain a charge of electricity 
produced by friction for some little time, because they are 
all non-conductors. The electricity stays on the surface 
where the friction is applied. It cannot flow to the hand 
and thence back to the earth. After a httle it oozes away 

26 






STATIC ELECTRICITY EXPERIMENTS 

into the air. It is easy to prove that a charge of static 
electricity cannot travel over the surface of a non-conductor. 
Rub one end of the glass rod with the silk and charge the 
bit of tissue-paper suspended from the silk thread. The 
paper will be instantly repelled by the charged glass. Re- 
verse the rod and extend the uncharged end toward the 
paper, and it will be instantly attracted. The charged rod 
and the charged paper must repel each other. But the end 
of the rod which has not been rubbed is not charged, there- 
fore the paper is attracted. The glass, being a non-conductor, 
does not permit the electricity of the charged end to flow to 
the uncharged end. 

To further illustrate the necessity of using non-con- 
ductors, try to perform these experiments with a metal rod. 
Any attempt to charge the metal rod will fail. The static 
electricity generated by rubbing the metal will escape as 
fast as it is produced. Insulate the metal rod by protecting 
it from the hand with a rubber glove, and it can be easily 
charged and made to perform the same experiments as the 
glass rod. 

To prove that there are two phases of the static charge, 
positive and negative, secure a stick of sealing-wax, and make 
a small flannel bag to fit over half of the stick. This bag 
must have a silk thread attached to the bottom, so it can 
be withdrawn without disturbing the electrical charge. 
Fit the bag on the stick and rub it up and down for a few 
seconds. Withdraw it by pulling on the insulating silk 
thread. Hold the wax to the suspended paper, which has 
been previously charged from the sealing-wax, and the 
paper will be instantly repelled. This shows that both the 
wax and the paper are charged with one phase of the static 
current, which is negative. Now present the flannel bag to 
the paper, and it will be instantly attracted, proving con- 

27 



HARPER'S BEGINNING ELECTRICITY 

clusively that the cloth is holding a different charge, which 
must be positive. This shows that both conditions always 
exist, one in the rubber and one in the substance rubbed. 
Sometimes the rubber is positive^ and the rubbed negative. 
The very next material tested may reverse this order, but 
the two charges are always present. 

It is very interesting to note the number of materials 
which are positively charged when rubbed with one substance 
and negatively charged when rubbed with another. When 
two pieces of the same material are rubbed together the 
smoother piece will be positively charged and the rougher 
negatively charged. If two pieces of silk are drawn against 
each other the position of the charges will depend upon the 
direction of the silk threads in the cloth. A great many 
experiments of this nature are possible. 

The Electroscope 

In order thoroughly to investigate the nature of these 
electrical charges, and to detect the presence of electricity 
in the different materials investigated, it will be necessary 
to make a better and more sensitive device to indicate the 
presence of electricity. Such an instrument is called an 
electroscope. The very simplest one is but a tiny ball of 
dry pith suspended from a very delicate silk strand unraveled 
from silk yarn. This must be mounted on a wooden frame. 
In a small block of dry wood bore a hole to admit a wooden 
upright twelve inches high and half an inch in diameter. 
Bore a small hole through the upright, near the top, and 
glue in a six-inch arm, a quarter of an inch in diameter, for 
the suspension of the silk thread and ball. Use no nails 
in making this "gallows" frame, and be sure the wood is 
dry (Fig. 2). 

28 



STATIC ELECTRICITY EXPERIMENTS 



Fig. 2 



Pith is easily obtained from an elderberry stick, or from 
the inside of a large corn-stalk. It can be fashioned into 
shape with a sharp knife. To fasten pith balls to silk threads 
touch them with just a tiny bit 
of mucilage. 

The most sensitive electroscope 
known is made of two pieces of 
imitation gold - leaf, such as is 
used by bookbinders and sign- 
painters. The strips should be 
about an inch wide and two 
inches long, or a single strip, of 
twice the length, doubled. Gold- 
leaf must be handled with the . 

greatest care, as it is very deli- I 

cate. It is best to have the 
pieces cut by the sign-painter or 
bookbinder, as they know how to handle it. The pieces 
of gold-leaf are so delicate that they must be suspended in a 
glass bottle to protect them from air currents. Aluminum- 
foil is quite as good as gold-leaf, and it is easier to handle. 
Its lightness makes up for its being somewhat thicker. Tin- 
foil is too thick and heavy. Gold-leaf and aluminum-foil 
can be cut by placing the leaf between sheets of heavy paper 
and cutting with a very sharp pair of scissors. Handle the 
foil, or leaf, with a warm sheet of writing-paper which has 
been slightly electrified by rubbing it with a silk cloth. The 
leaf will adhere to the paper and can be easily placed. 

A wide-mouthed bottle is used. A small brass rod is 
passed through the cork, and half-way down the inside of 
the bottle, where it is provided with a clasp or hook to hold 
the gold-leaf or aluminum-foil. The leaves must not touch 
the bottom. The top of the brass rod should be four or five 

29 



HARPER'S BEGINNING ELECTRICITY 



inches above the stopper, ending in a ball or ring. It is 
always best to insulate this rod from the cork or stopper. 
This can be done by boring a hole through the cork some- 
what larger than the rod and surrounding the rod with sulphur 
or sealing-wax melted and poured into the hole. A Httle 
pasteboard disk fitting tightly against the bottom of the 
cork will keep the melted wax from running through into the 

bottle. It is obvious that the 
rod should be made and placed 
before the gold-leaf is installed. 
A metal clasp can be used to 
hold the gold-leaf, or it can be 
pasted in a slot cut in the end of 
the rod (Fig. 3). The gold-leaf 
can be a single piece doubled 
over a hook on the lower end of 
the brass rod. 

The gold-leaf or aluminum- 
foil electroscope, when properly 
made, is very sensitive. When- 
ever an electrified body is brought 
near the instrument, without ac- 
tually touching the brass rod, the 
gold-leaves will diverge. This is 
due to the fact that they are 
always charged alike, and, there- 
fore, repel each other in propor- 
tion to the charge excited. 
It is generally desirable to provide narrow strips of tin- 
foil down the inside of the bottle, up through the top, and 
down the outside to the bottom, so the leaves will discharge 
themselves when fully distended. 

A pencil pulled through the fingers will excite the leaves. 

30 




Fig. 3 



STATIC ELECTRICITY EXPERIMENTS 

Fleshly torn cloth will show a charge of electricity. Waving 
a feather duster through the air across the room from the 
electroscope will diverge the leaves if the atmosphere is 
right. Tapping the finger on the table, pulling ofF a glove, 
taking out a pocket handkerchief, tearing a piece of paper, 
vibrating a taut string, all show that electricity is present. 
The amount of electricity produced by any one of these 
experiments is very, very small, but the delicate electro- 
scope will detect its presence. 

The electroscope should be used only to detect weak 
electric charges. If subjected to a violent discharge the 
delicate leaves may be torn and broken. 

There is really no limit to the experiments possible with 
a good electroscope, and it adds much interest to the study 
of static electricity. The instrument is easily and cheaply 
made. Even if the gold-leaf electroscope is not available, 
a sufficient number of interesting experiments can be made 
with the suspended pith ball. 

It was long thought that static electricity collects only 
on the surface of materials. Faraday attempted to prove 
this by building a large hollow sphere of wood covered in- 
side and outside with tin-foil. He shut himself up inside 
this hollow ball with his instruments, while his assistants 
charged the outside with static electricity. Faraday could 
not detect any electricity on the inside of the globe, even with 
the most delicate instruments his ingenuity could devise, 
although the outer coating was heavily charged and gave 
forth brilliant sparks. 

A very simple experiment will show that static electricity 
always frequents the outside of any material. Mount a 
small conical muslin bag on a hollow ring which is held 
upright in a glass bottle for insulating purposes. A silk 
thread is fastened to the small end of this bag, so it can 

3t 



HARPER'S BEGINNING ELECTRICITY 

be turned inside out at will by simply pulling the thread 
(Fig. 4). 

Charge this bag on the outside by touching it a number 
of times with the hard rubber, or glass rod, which is elec- 



trically excited by friction. When the bag is thoroughly 
charged test it with the electroscope. The outside will show 
a heavy charge of electricity. Test it on the inside with the 
aid of a brass rod, and it will show no electricity. Now pull 
the silk thread and turn the bag inside out. What was the 
outside is now the inside; but, strange to say, the electro- 
scope will show that the electricity is still on the outside of 
the bag. Turn the bag again, and the charge will go to the 
outside. This experiment can be repeated as long as the 
charge lasts. d 

Only a few of the countless static experiments possible 
are mentioned here, and it rests with the ingenuity and in- 
terest of the experimenter to devise and test as many as 
desired. 

Lines of Force 

Every static charge is surrounded with invisible "rays" 
which extend for a considerable distance out in the air. 
These "rays," or lines of force, account for the attraction and 

32 



STATIC ELECTRICITY EXPERIMENTS 

repulsion of charged bodies. The rays really attract all un- 
charged bodies, but they are so feeble in strength that 
only the very lightest materials, such as pith, bits of paper, 
etc., are drawn toward the source of the invisible "rays." 
Fig 5 illustrates lines of force about a glass rod, the end of 
which holds a charge of static electricity. 




If the attracted body is not brought into actual contact 

with the charge, it is certainly influenced and affected by 

the presence of the charged body and the lines of force 

which reach it. This invisible influence which surrounds 

a charged body, extending a certain distance in every di- 

I rection and affecting everything within its reach, can induce 

I a charge on other bodies. This process of transmitting a 

I charge is called induction. Induction means to influence, to 

I bring on, to cause. 

Bring an electrified body near the gold-leaf electroscope, 
without actually touching it, and the leaves will diverge. 
Remove the charged body, and the leaves will converge 
again. This shows that a charge of electricity has been 
induced in the gold-leaves by the presence of an electrified 

33 



HARPER'S BEGINNING ELECTRICITY 

body, otherwise they would not repel each other, as similarly 
charged bodies should. 

Even if a sheet of paper, glass, or a piece of cloth be 
placed between the charged body and the electroscope, the 
effect will be the same. 

It is not definitely known just how this inductive force 
is transmitted through the air. Perhaps it is not necessary 
to know this, inasmuch as we know the principle and the 
effects. But it is well to give careful thought and study to 
this wonderful problem of induced currents, as they are 
employed in a great many different ways in modern elec- 
trical machinery and apparatus. 



i; 



Chapter V 

STATIC ELECTRIC GENERATORS 

IT is hardly possible to secure enough static electricity 
for elaborate experiment by rubbing glass or amber with 
a silk handkerchief. The glass rod and pith ball are all 
right for studying the first principles and general char- 
acteristics of a static charge. But, for larger demonstra- 
tions, a machine which will generate, or produce, a good 
supply of static electricity is quite necessary, 

Volta invented the simplest of all static generators. He 
called it an electrophorus. It is, perhaps, easier to make the 
device than it is to pronounce the name. This was a dis- 
tinct improvement over the sulphur and glass globes used 
by Von Guericke and Isaac Newton. 

Volta's electrophorus consists of two metal disks and a 
cake of resin. A very good one can be made with a shallow 
metal pie-tin about ten inches in diameter. Place the tin 
on the back of the stove, where it is not too hot, and fill it 
with powdered resin. Resin is very cheap, and can be 
purchased at any drug store. As the resin gradually melts 
keep adding to it until the dish is nearly level full, then pull 
it to one side where it will cool slowly. Be sure to use a 
metal dish, as granite-ware will not work. If any impurities 
come to the surface, skim them off so the resin will be smooth 
when cool. 

The second part of the apparatus can be either a thin, 
3 35 



HARPER'S BEGINNING ELECTRICITY 

flat disk cut from sheet tin, or a thin wooden disk well cov- 
ered with tin - foil. The latter is easiest and cheapest to 
make. Cut from soft wood a circle an inch less in diameter 
than the tin, and half an inch thick. This disk must be 
level and wery smooth. Cover co7?ipletely, both sides and 
edges, with tin-foil pasted in place. Lay the foil nice and 
smooth. The finished disk must now be provided with an 
insulated handle. This is easiest made from a stick of 
sealing-wax. Warm one end of the wax until it is soft, 
and press it firmly down on the center of the wooden disk. 
When it cools it will stick there tight enough to be used as 
a handle. If the tin-foil is removed for a little space and 
the wood roughened, the wax will stick better. A better 
and stronger handle can be made of wood if it is completely 

«€-lNSULATED HANDLE 



^ ^TINFOIL DISK 



^==^- 



Fig. J 



PIE TIN HOLDING 
RESIN CAKE 



covered with glass, rubber, or some other good insulatmg 
material. A wooden handle 7nust be insulated from the 
hand (Fig. i). 

To use the electrophorus the resin in the pie-tm must be 
sharpl}^ whipped for a few seconds with a silk cloth or a 
piece of fur. Cat's skin makes the best exciter, although an}- 
bit of soft fur will answer. Beat the resin briskly, yet not 
hard enough to crack or break it, then place the tin-foil 
cover on the resin. Be careful not to touch the cover to the 

36 



STATIC ELECTRIC GENERATORS 

edge of the metal disk. As it is an inch less in diameter, it 
can be easily put in place without touching. Now touch a 
finger to the upper side of the cover. Remove the finger 
and lift the cover by the insulated handle. You will find 
that a large bright spark can now be secured from the 
cover. Place the cover back on the resin as before and 
touch it again with the finger. After removing the cover 
you can secure another bright spark. This operation can 
be repeated a great many times without recharging the 
resin. 

The action of the electrophorus can be improved by con- 
necting the outside of the pie-tin to the floor by a small 
chain or wire. This helps to complete the circuit. At no 
time should the cover be allowed to touch the tin while the 
device is being used. If it touches the resin must be re- 
charged. This simple generator can be used for very exten- 
sive experiments with static electricity. 

The explanation of the electrophorus is not so easy. The 
static charge on the cover is produced by induction. This 
is why it can be repeated time and again without exciting 
the resin each time. When the resin is struck with the silk, 
or fur, then it becomes charged with negative electricity. 
When the finger is touched to the cover it completes the cir- 
cuit and the cover becomes charged with positive electricity. 
It will sometimes work better if the chain from the pie-tin is 
held in the hand while experimenting. Otherwise the in- 
sulating properties of the table may prevent the current 
from passing from the tin to the cover. Usually this charge 
will pass over the table and floor and through the body, via 
the finger, to the cover when it is touched before being 
removed. 

The electrophorus should always be kept in a warm, dry 
place, free from dust and dirt. It will produce more elec- 

37 



HARPER'S BEGINNING ELECTRICITY 

tricity if it is slightly warmed before using. Do not get it 
warm enough to soften the resin. 

The Glass -Cylinder Generator 

A very good static generator can be easily constructed 
from a large glass bottle. Select a round, smooth quart 
bottle (or larger, if possible) the body of which is nearly 
cylindrical. Do not use a bottle with a long, tapering neck. 
Clear glass is always best. Bottles with names, trade- 
marks, etc., blown into the glass should not be used. 

To prepare the bottle for the machine it must be pro- 
vided with axles, so it can be mounted in a frame and ro- 
tated. The neck of the bottle will answer very well for 
one axle. For the other a hole must be made in the bottom, 
or the glass can be roughened with a piece of emery paper 
and a large spool cemented in place. A hole can be cut 
through the bottom of the bottle with a glass-cutter. It 
can be ground through with an emery drill, or it can, some- 
times, be punched in with a steel punch. Strike the punch 
a sharp blow, driving it quickly through the glass, and 
work the hole carefully to the desired size. Very often the 
bottle will break during this process. The safest way is to 
cement a large spool to the glass. Cement is made especial- 
ly for fastening things to smooth glass, but it will always 
stick better if the glass is roughened. Heavy furniture glue 
can also be used to fasten the spool in place if the glass is 
first made rough and then warmed before the glue is applied. 

If a hole is worked through the bottom of the bottle it 
should be in the center, and approximately the same size - 
as the mouth of the bottle, so that a wooden shaft can be 
extended through it for mounting in the wooden frame. 

Assuming that the spool method is used, a wooden plug 

. 38 



STATIC ELECTRIC GENERATORS 

must be fitted and cemented in the mouth of the bottle. 
Square it off at the outer end for the crank-shaft. The 
crank should be short, so it can be turned fast. It should 
be about six inches long, fitted with a wooden handle. A 
square hole must be cut in the end for fitting to the square 
"cork" in the bottle. The bottle, with spool and crank in 
place, is now ready to be mounted in a wooden frame so 
that it can be rotated. 

The wooden frame consists of a baseboard about ten by 
fifteen inches, and an inch thick. The exact size of this 
board will depend, of course, on the size of the bottle used. 
There must be four uprights about eight inches high and 
two inches square. Four pieces of pine board, two inches 
wide and half an inch thick, will complete the frame. The 
four uprights are set in holes bored near the four corners of 
the baseboard. The pieces of board are nailed along the 
top of the uprights to complete the frame. Two semi- 
circular notches are cut in the middle of the frame at each 
end to admit the spool and the neck of the bottle. Even 
though the wood is very dry, it is better to line these grooves 
with melted sealing-wax, pressing the bottle in place just 
before the wax cools, for insulation purposes. 

The bottle can now be whirled with the aid of the crank. 
To generate static electricity friction must be applied to its 
surface. This is accomplished by a leather-covered wooden 
block set in the frame so as to press against the glass. The 
block should be two inches wide, slightly hollowed to conform 
with the curvature, and the same length as the cylindrical 
part of the bottle. A little felt, or thick cloth, is laid over 
the block, and then a soft leather cover, cut from an old 
glove, is folded over and tacked to the back. This pad is 
mounted on a metal rod which passes through the wooden 
frame and admits of adjustment to any desired pressure. 

39 



HARPER'S BEGINNING ELECTRICITY 

When the crank is turned the leather friction-pad rubs 
against the glass and produces static electricit}^ This elec- 
tricity would stay on the glass if it were not picked up and 
carried ofF by a "collector" as fast as it is produced. 

The "collector" is made of a thin strip of wood through 
which has been driven a row of small, sharp-pointed brass 
tacks about half an inch apart. The heads of these tacks 
are connected by a fine brass wire. It is mounted on a rod. 
This rod passes through a small hole in the frame on the 
opposite side of the bottle from the rubber, so that the 
sharp brass points just touch the rotating glass. The end 
of the rod should terminate in a ball, or a ring, so that the 
electricity cannot ooze away into the surrounding atmos- 
phere, as it is very like to do where a sharp point is con- 




SJLK CURTAIN 

RUBBER 




SIDE PIECE NOTCHED FOR SPOOL OR 
BOTTLE NECK AND LINED WITH WAX 



COnPLETE BOTTLE HACHINE 

Fig, 2 B 



Fig, 2 A 



venient. Now a silk curtain should be made to extend from 
the leather pad over the top of the glass almost to the brass 
points of the collector. This curtain can be sewn to the 
edge of the leather pad. Its purpose is to keep the elec- 

40 



STATIC ELECTRIC GENERATORS 

tricity on the glass until it is picked up by the collector. 
Fig. 2 A shows parts of static machine, and Fig. 2 B the 
complete static machine. 

To operate this machine be sure that it is perfectly dry. 
A few minutes in a large oven will make certain of this. 
The brass ring from the "rubber" pad should be connected 
to the "ground" by a small chain, or wire, and the machine 
is ready for operation. "Ground" in this case does not 
necessarily mean the earth. Generally the floor will 
answer. 

When the crank is turned the friction of the pad on the 
surface of the glass produces a steady supply of static 
electricity. This is kept on the glass by the silk cloth until 
it is picked up by the sharp points of the collector. After 
the machine has been operated a minute or two an object 
brought near the collector-ring will draw from it a large, 
brilhant, crackling spark. This machine will produce more 
electricity if the soft leather pad is rubbed with a little 
mercury amalgam scraped from the back of an old looking- 
glass. 

The bottle static machine is amply large enough for all 
practical purposes. It will produce enough electricity to 
conduct a large number of interesting experiments. But 
a larger and better static machine can be made from a 
circular disk of window-glass. 

The Glass -Disk Static Generator 

The glass-disk machine is a trifle harder to make, but it 
will reward the experimenter with an abundance of static 
electricity. The only vital diff'erence between the glass-disk 
machine and the bottle machine is in the shape of the 
"rubber" and the "collector," which must operate on both 

41 



HARPER'S BEGINNING ELECTRICITY 

sides of the glass. By using a disk both surfaces of the glass 
can be used, thus doubling the power of the machine. 

The clerk where window-glass is sold can easily cut out 
a circular disk of glass fifteen inches in diameter. By draw- 
ing a circle of that diameter on a clean sheet of paper, lay- 
ing the glass on the paper, and running the glass-cutter 
along the pencil-mark, a fairly true circle can be cut. It is 
always better to cut an inch hole through the center of the 
glass disk; but this is not absolutely necessary. Such a hole 
adds strength to the machine. It can be worked through 
the glass with a good glass-cutter. Mark out an inch 
circle on a piece of paper. Lay the glass over this until it is 
well centered and cut on both sides. Make a perforation 
through the glass by "rocking" the cutter back and forth. 
As soon as a hole is worked through it can be broken away 
to the inch circle already marked on both sides. 

In case it is not advisable to cut a hole through the glass, 
and it is very apt to break during the operation, wooden 
disks can be cemented on either side for its suspension in 
the frame. Prepare two wooden disks an inch and a half 
thick and three inches in diameter. Bore a three-quarter- 
inch hole through the center of each disk, and glue in the 
round shafts for the axles. The round shaft should project 
about three inches from the wooden disks. Roughen the 
glass with emery-paper about the center for the size of the 
disks and glue, or cement, them firmly in place. Be sure to 
have the shafts well centered so the disk will whirl true. 
While the wooden disks are drying in place the frame can 
be built. 

This frame must be made of dry wood, so that the glass 
disk is held upright, suspended from the axles, and free to 
turn at considerable speed. The frame should be ten inches 
high, four inches wide, and eighteen inches long. This will 

42 



,/ i/////////////77777777/yV////^J/ y'' 



FRAME FOR RUBBER PAD 




QLASS DISK WITH SIDE 
PIECES AND CRANK SHAFT 



COLLECTOR 




Fig. 4 

GLASS-DISK STATIC MACHINE 



HARPER'S BEGINNING ELECTRICITY 

allow the glass disk to set in place and clear the ends and 
bottom. Care must be taken to make this frame strong and 
rigid. If it "gives" and "creeps" it will certainly break 
the glass disk. 

The glass is hung upright in the frame, turning freely on 
the axles. It is whirled with a small wooden crank, or a 
pulley wheel and round belt. The notches for the axles 
should be lined with sealing-wax melted and pressed into 
place. The "rubber" and "collector" for this machine 
must be made U-shape, so as to work on both sides of the 
glass. The rubbing-pad is really two pads six inches long 
and two inches wide, covered with soft leather, and fastened 
together at one end. This rubber is fastened to a metal 
rod and mounted to the frame, so that it pinches tightly 
against the glass on either side. The collector is but two 
thin strips of wood, through which have been driven sharp- 
pointed brass tacks at an interval of half an inch or less, 
all connected with a small brass wire, and mounted on a 
metal rod. The rod passes through the wooden frame on 
the opposite side from the friction-pad, and terminates in 
a ring or ball. Two silk curtains must also be made for 
this machine, to extend from the leather pad on both sides 
of the glass to a point near the collector. Fig. 3 shows the 
parts of the glass-disk static machine, and Fig. 4 the machine 
with side-piece outlined to show friction-pad and collector. 

The leather friction-pad should be "grounded" to the floor 
with a small chain, or wire, and the machine is ready to pro- 
duce static electricity. A Kttle mercury amalgam for the 
leather pads will increase the flow of electricity to a marked 
degree. 

Brilliant sparks of considerable length can be secured from 
the collector-ring of this machine, and it is suitable in every 
way for all kinds of static experimental work. 

44 



STATIC ELECTRIC GENERATORS 

There is still another kind of a glass-disk machine for the 
production of static electricity. This machine produces 
static electricity by induction, instead of by friction. It re- 
quires two glass disks, with several perforations, and is very 
expensive and hard to build. It is more powerful than any 
other static machine, but the two generators mentioned are 
good enough for all practical purposes. 



Chapter VI 

EXPERIMENTS WITH THE STATIC MACHINE 

GLASS rods, rubber plates, sticks of sealing-wax — all 
will be quickly laid aside when the static machine is 
ready for operation. Instead of tiny sparks, visible only 
in the dark, an abundance of static electricity can now be 
secured. 

Sparks of great length, of various shapes and sizes, leap 
and crackle from the collector-ring when the machine is 
in operation. Such a supply of static electricity makes it 
possible to try out endless experiments. 

The static generator is frail at best, and should always 
be handled with care. Where the axles are merely cemented 
in place this is especially true. Remember that glass cyHn- 
ders and disks are easily broken. Be sure that the machine 
is dry and warm before using. A damp, cold machine will 
not produce good results. It is best to stand it near the 
fire for a few minutes, until it is thoroughly warm. 

It is not necessary to turn the static generator at high 
speed. A steady, brisk movement of the crank-handle will 
suffice. The friction-pad and the collector should be nicely 
adjusted before starting. The soft leather pad, coated with 
a film of mercury amalgam (mercury and tin mixed to a 
paste), should rub firmly, and yet not too hard against the 
glass. The silk curtains should lay close to the surface of 
the glass, almost touching the collector-points. The brass 

46 



STATIC MACHINE EXPERIMENTS 

points of the collector should just touch the surface of the 
glass, with the least friction possible. 

Do not forget that electricity always travels in a complete 
circuit. Static electricity is always under high pressure, or 
potential, and usually it will flow through the frame of the 
machine, the table and the floor to complete its circle. 
But, often enough, the table is so dry that it is a fairly good 
non-conductor, for even such high potential, and the generator 
will not work well in consequence. It is better to fasten 
a small brass chain, or even a wire, to the brass ring of the 
friction-pad, or negative pole, and allow it to dangle on the 
floor. This is not always necessary, however, as the high 
pressure will usually force its way over the intervening wood. 

Whirl the crank for a few seconds, and a long, brilliant 
spark can be secured from the collector-ring. This static 
electricity is produced by the friction of the leather pad on 
the dry glass. The silk curtain carries the current to the 
collector, where it is picked up by the brass points and 
accumulates on the brass rod and ring. When your finger 
approaches the brass ring, which is positively charged, the 
electricity readily jumps the intervening air-space, races 
through your body, across the floor and up the table legs 
to the negative pole of the machine. 

Analyzing the Static Spark 

Static sparks are best observed in a darkened room. 
Many remarkable variations of the spark will be noted. 
When a metal object is brought very near the collector-ring 
the spark will take a straight course through the air. As the 
distance is increased the spark begins to zigzag, like minia- 
ture lightning. Finally, when the distance is considerable, 
it discharges in brush form, like a tree with many branches. 

47 



HARPER'S BEGINNING ELECTRICITY 

The short spark will be of dazzling whiteness, emitting a 
bright flash of light. The brush discharge will have a 
bluish tint, showing that it is not so hot as the shorter spark. 

The static spark deserves close analysis. Air is, generally 
speaking, a non-conductor of electricity. The air-space cov- 
ered by the spark is called the air-gap. Electricity cannot leap 
across an air-gap unless it has enough pressure, or potential, 
behind it to destroy, or break down, the non-conducting 
properties of the air. The pressure or potential of an electric 
current is expressed in volts. It has been demonstrated by 
experiment that it requires a pressure of at least twenty 
thousand volts to leap across one inch of air-space. There- 
fore, if the static machine will produce a spark which will 
leap across one inch of air-space it may safely be assumed 
that the electricity possesses a pressure or potential of 
twenty thousand volts. The quantity of electricity is very 
small, but it is under heavy pressure. 

With this enormous pressure behind it, traveling at the 
terrific speed of i86,i6^ miles a second, the electricity 
plunges through the air-space, literally burning it up in its 
passage. The molecules of the air are instantly heated to 
incandescence and give a brilliant flash of flame. This 
destruction of the air produces a tiny vacuum which is 
quickly closed by the pressure of the atmosphere, which is 
about fifteen pounds to the square inch. The closing of this 
vacuum causes a concussion of the air which is plainly 
audible to our ears. This crackUng and snapping of the 
spark is nothing more or less than miniature thunder fol- 
lowing a miniature flash of lightning. 

The short, "fat" spark is also very hot. It will ignite 
powder, gas, vaporized gasolene, or naphtha. It will readily 
pierce several sheets of paper, leaving the edges slightly 
charred (Fig. i). 

48 



I 

I STATIC MACHINE EXPERIMENTS 

I The discharge from the static machine, when it is al- 

! lowed to pass through the body, will cause the muscles to 

I jerk and twitch. This in itself is not harmful, but it is very 

! disagreeable. It can be easily avoided entirely by using 

I a little device called a discharger. A suitable discharger 

can be made from a piece of heavy copper wire about thirty 

I inches long bent in a V shape. The ends of the wire should 

! be bent into rings or armed with small wooden balls well 

i covered with tin-foil. This tin-foil should be brought down 

and twisted firmly to the wire to insure a good connection. 

The wire should now be carefully wound with several layers 

of electrician's rubber insulating tape. To use the device 

one end of the discharger is placed on the chain dangling from 

the friction-rod, and the other end is brought closely to the 

collector-ring. The discharger is absolutely necessary for 

experiments with large quantities of static electricity (Fig. 2). 

Experimenting with Static Electricity 

Sparks several inches long are not unusual with a good 
machine. These sparks can be made to jump over ob- 
stacles in their path, thus increasing their briUiancy. Hold 
a strip of glass between the collector-ring and the discharger 
and the spark will easily jump over the non-conducting 
glass (Fig. 3). 

To understand how the passage of the static current burns 
up the molecules of the air it is only necessary to coat a 
four-inch sheet of glass with common varnish and dust it 
lightly with iron filings before it is dry. The filings must 
be as fine as possible. Edge the glass on two sides with 
narrow strips of tin-foil, so as to form a good connection 
with the filings. By holding the glass between the col- 
lector-ring and the discharger so the ring touches one strip 

49 



HARPER'S BEGINNING ELECTRICITY 



of tin-foil and the discharger the other, a briUiant spark 
will run rapidly over the glass, burning the filings as it 
passes. The spark will take various courses over the glass. 




Fig. 4 



as it seeks the easiest path where the filings are thickest 
(Fig. 4). This explains why long flashes, including light- 
ning, frequently travel a zigzag path. Filings from differ- 
ent metals will produce different luminous results. Brass 
filings will cause the light to have a greenish tinge; zinc 
fiUngs produce a bluish Hght. 

It is obvious that these experiments with the static spark 
should be carried out in a darkened room for the best effects. 

50 



STATIC MACHINE EXPERIMENTS 

The room need not be totally dark for this purpose. Enough 
light should be admitted to see to work the apparatus. A 
great many wonderful luminous effects will be noticeable 
when the static machine is operated in the dark. The 
friction-pad will glow with a soft greenish light, due, perhaps, 
to the mercury amalgam. Each brass point of the collector 
will be a bright star, and if the hand is brought near the 
collector a sheet of bluish flame will accompany the brush 
discharge between it and the collector-ring. If an old in- 
candescent lamp, which still has some vacuum, is brought 
near the collector it will glow with a strange light. A tube 
containing a little mercury, if shaken near the collector, will 
also glow with light. Tiny brush discharges will take place 
from all sharp corners of the machine, strange and mysteri- 
ous sparks will flash about as the charge becomes heavier 
and heavier. 

Static discharges are mostly flash and noise. Ordinary 
discharges from the machine are perfectly harmless. A 
number of persons can join hands and take a "shock" from 
the static machine with perfect safety. Indeed, all experi- 
ments with the static machine are distinctly beneficial in' 
one way. The discharge of the current through the air 
produces a gas known as ozone. This gas, more or less akin 
to oxygen, is an active destroyer of odors and organic matter 
of all kinds. Ozone is colorless, and it has the peculiar 
property of destroying noxious organic particles, bacteria, 
and germs in the air. It burns them up and reduces them 
to harmless water and ash. This is exactly the same kind 
of ozone advertised by the seashore and mountain health 
resorts. Many years ago the presence of this gas was 
noticed when the static generator was in operation. Those 
early pioneers in electricity did not know what it was, and 
spoke of it as "the smell of electricity." This "smell" is 

4 SI 



HARPER'S BEGINNING ELECTRICITY 

also noticeable in the air immediately after a flash of light- 
ning. It is ozone, instead of sulphur, which greets the nos- 
trils after a severe thunder-shower. Electric machines for 
producing ozone gas are now in every-day use in theaters, 
public halls, subways, offices, factories, and other places 
where people congregate. They are used to keep the air 
pure and sweet. 

Storing Static Electricity 



I 



Benjamin Franklin invented one of the first devices for 
accumulating, or storing, static electricity. To make a 
similar one take a sheet of common window-glass eight by 
ten inches, and paste a sheet of four-by-six tin-foil on each 
side of it. This should leave a two-inch space all round 
the glass for insulating purposes. The glass should then 
be set upright in a groove in a wooden base (Fig. 5). Con- 
nect the tin-foil on one side of the glass with the collector- 
ring, using a short insulated wire for the purpose. A wet 
string can also be used, as it is a fairly good conductor of 
high-potential electricity. Connect the tin-foil of the other 
side to the friction-pad in the same way and start the ma- 
chine. Positive electricity will rapidly collect on one sheet 
of tin-foil and negative electricity on the other. These 
forces are constantly striving to equalize, but the glass keeps 
them apart. Soon the pressure will become so great that 
the electricity will leap around the glass, over the four-inch 
air-gap, with a flash of light and a loud report. After it has 
discharged itself in this way the experiment can be repeated 
indefinitely. 

The power of the Franklin accumulator can be increased 
by using a number of glass plates and sheets of tin-foil 
arranged in a stack. Begin the stack with a glass plate six [ 

52 



STATIC MACHINE EXPERIMENTS 

by eight inches, then a sheet of foil four by six inches. Lay 
the foil so that one edge extends out over the glass on one 
side. Cover with a sheet of glass and add another sheet of 
foil extending out on the opposite side. As many sheets 
can be added as desired, laying the foil carefully so that 
their ends extend out first on the left and then on the right. 



TIN FOIL 




Fig. 5 




INSULATINq TUMBLER 



Fiff. 6 

Five or six sheets will be sufficient. End as you began, 
with a sheet of glass. Pinch the foil ends together on the 

53 



HARPER^S BEGINNING ELECTRICITY 

left-hand side and connect to the positive pole of the ma- 
chine. Pinch those on the opposite side together and con- 
nect to the negative pole. The stack should be placed on a 
glass tumbler for insulation purposes (Fig. 6). 

This pile is properly called a condenser because it con- 
denses, or accumulates, electricity. When this condenser is 
fully charged a cascade of discharges will flow over the 
edges of the glass. Sparks of remarkable length can also be 
obtained with the aid of the discharger. 

In handling this device be careful not to discharge it 
through your arms, as the jolt will be severe and your arms 
will be jerked so that the plates may be broken. Always 
use the discharger. 

The Leyden Jar ! 

For all experimental purposes with static electricity the 
Leyden jar is best. The Leyden jar was discovered quite ) 
by accident many years ago in the city of Leyden. It is | 
also an accumulator or condenser, but its form makes it ideal f 
for experimental purposes. I 

A suitable Leyden jar can be made from any large- i^ 
mouthed glass bottle. A jelly jar, or pint fruit can, will be jj 
suitable. Line the jar half-way up on the inside, including P: 
the bottom, with tin-foil. Ordinary paste will hold the foil * 
in place. Paste tin-foil on the outside for the same dis- j 
tance, including the bottom. Fit a cover of dry wood to \ 
the jar through the center of which is bored a half-inch hole. 
A brass or copper rod, made from heavy wire, is arranged \ 
to pass through this hole in the cover. This rod should be 
long enough to touch the bottom of the jar and to protrude 
at least four inches above the cover. The top of the rod !^ 
should terminate in a ring, or, better still, a wooden ball f 

54 



STATIC MACHINE EXPERIMENTS 



nETAL ROD 

,4- INSULATING COVER 



_.- CHAIN 



-TINFOIL 
INSIDE & OUT 



I covered with tin-foil. The metal rod must now be insulated 

from the wooden cover. This can be done by arranging 

I a pasteboard disk on the rod just under the wooden cover, 

I and pouring the space between the rod and the cover level- 

I full of melted sealing-wax. Be sure that the lower end of 

I the rod touches the tin-foil on 

I the bottom of the jar. This 

is made certain by fastening 

a bit of chain or wire to that 

end of the rod (Fig. 7). 

The Leyden jar is charged 
by holding or connecting the 
brass rod to the collector of 
the static machine, while the 
outer coating of the jar is 
held in the hand, or con- 
nected to the friction - pad 
with a short wire. 

It is well to avoid a dis- 
charge from such a jar. The 
"jolt" is very heavy, al- 
though not dangerous. No electricity is produced by the 
jar. It is merely an accumulator. Electricity cannot be 
stored in the jar for long periods, as it gradually "leaks" 
away into the surrounding air. 

Always use the discharger in experimenting with Leyden 
jars. 

The current stored in such a jar is under heavy pressure. 
If your hand should happen to come near the rod the jar 
would instantly discharge itself through your body, even if 
you did not actually touch the outer coating. In such 
cases the current is heavy enough to run through your body 
to the floor, along the floor to the table, and up through 

55 




Fig^ 7 



HARPER'S BEGINNING ELECTRICITY 

the table to the outer coating. Even dry wood is not a 
good insulator for high-pressure static currents. If the jar 
is placed on an insulated glass standard such a discharge 
is impossible. If you touch the knob then only a little spark 
will result. 

When a Ley den jar is charged one of the tin-foil coatings 
is positively and the other negatively electrified. The jar 
cannot be charged if placed on an insulated stand, unless 
the circuit is made complete. The inside coating must be 
connected in some way to the collector of the generator 
and the outside coating to the friction-pad, or vice versa. If 
such a circuit is not readily established through the table 
and floor, see that it is completed with a wire or wet string. 

TO COLLECTOR 







The capacity of a jar depends upon the extent of the 
tin-foil surfaces and the thickness of the glass. Thick glass 
affords too much resistance to the charge and should not 
be used. Ordinarily the inner foil is positively charged, and 
the outer negatively. This is not always true, however, as 
it will work well both ways. These charges are kept apart, 



STATIC MACHINE EXPERIMENTS 

or insulated, by the glass. If you pick up a small jar, 
slightly charged, holding it by the outer coating, and touch 
the finger to the knob the circuit will be completed and 
the jar is said to be discharged. In this case the current 
will run through your arms from the higher potential to 
the lower potential — from the positive to the negative plate. 

Heavy sparks from the Leyden jar will perforate glass, 
thin books, newspapers, bits of wood, etc. They will leap 
across long air-gaps. If one jar does not give enough elec- 
tricity for an experiment others can be made and used with 
it by placing them in series or cascade (Fig. 8). This means 
that a number of small jars can be so arranged that they 
will act as one large jar. When arranged this way the 
positive plate should be connected with the negative plate 
of the next jar — the inside of the first jar with the outside 
of the second jar. They can also be arranged by connect- 
ing all the positive plates and setting the jars on a metal 
plate which connects all the negative plates (Fig. 9). 

One of the most interesting experiments with the static 
machine is to charge an insulated person with static elec- 
tricity. A good insulating stool can be made by placing 
a small board on four inverted glass tumblers. The person 
is given a wire to hold which is connected to the collector- 
ring of the static generator. The subject will not be hurt 
or inconvenienced in any way. After the machine has been 
operated for a few minutes it is easy enough for the person 
so charged to reach up and light the gas with a spark from 
the finger. Long, brilliant sparks can be produced at will. 
Any one touching the person will be greeted with a spark 
and a muscle-twitching "jolt." The hair of the subject's 
head will have a tendency to stand on end, and, if dark, 
the sharp edges of all metal objects will glow with escaping 
electricity. 



Chapter VII 

FURTHER EXPERIMENTS WITH STATIC ELECTRICITY 

STATIC electricity readily escapes from a sharp metal 
point in the form of a brush discharge. It seems to 
spray ofF into the air with very little, if any, light, and with- 
out noise. This rush of electricity from the needle-point 
produces a sharp current of air which can be readily observed 
by approaching the point with a candle-flame. The flame 
will be blown aside as by a puff* of air. 

A very novel little toy "motor" can be made by taking 
advantage of this escaping electricity. Take two small 
wires three inches long and solder them together in the form 
of a cross. After sharpening the ends with a file bend the 
points over at right angles, taking care to bend them all the 
same way. The center of the wires should be somewhat 
flattened with a file and indented a bit with a punch, so 
that the device can be balanced on a pivot point so as to 
turn freely. It should be mounted on an insulated base. 
Sticking the pivot wire in a cake of wax is sufl&cient (Fig. i). 

When the pivot standard is connected to the collector 
of the static-generator the electricity will flow out on the 
metal arms and escape from the sharp points. The re- 
actance of this escaping electricity, pushing against the air, 
will whirl the "spider" as long as the current flows to it. 

Magnets can be made from static electricity. This 
proves that static is of the same nature as electrical currents 
produced in other ways. 

58 



FURTHER EXPERIMENTS 

To magnetize steel needles and steel bars with a static 
machine a coil of insulated copper wire must be provided. 
By winding the wire tightly over a round stick, and then 
withdrawing the stick, a coil or helix can be easily made 
(Fig. 2). This coil is placed on a glass insulator or sus- 
pended from silk cords. The needles or steel bars to be 
magnetized are merely laid in this coil or helix, while several 
charges of electricity are sent through the wire by connect- 
ing one end to the ground and placing the other very near 
the collector-ring of the static-generator. The discharge 
from a Ley den jar will also serve to magnetize the steel. 




Fig.t 

A great many interesting experiments can be tried with 
the Leyden jars to determine the strength of the static cur- 
rent. A little device should be made to act as a fixed dis- 
charger for these experiments. This will eliminate any un- 
pleasantness which might occur from becoming too familiar 
with a heavy charge. The discharge from an ordinary 
Leyden jar is not dangerous, but it is certainly surprising 
when it comes unexpectedly. 

To make the fixed discharger secure two short bottles. 
Place a heavy brass or copper wire twelve inches long through 
each cork. A tin-foil ball is fixed to one end of each rod, 

59 



HARPER'S BEGINNING ELECTRICITY 



and the other end is bent into a ring so it can be connected 
by an insulated wire to the terminals of the static machine 
or the opposite poles of the Leyden jar (Fig. 3). 

Connect one part of the discharger to the outside coating 



n 



o o 




Fig, 3 



of the Leyden jar. Connect the other to the inside coating. 
Charge the jar in the usual way. When the opposing balls 
of the fixed discharger are moved near enough to each other 
a discharge will take place. The distance necessary to dis- 
charge the jar will depend, of course, on the amount of elec- 
tricity present and the pressure stored up in the jar. If 
there is about 20,000 volts a discharge will take place across 
one inch of air-gap, and so on. 

It is surprising to note the force of this discharge. If a 
sheet of cardboard be placed between the discharger-knobs, 
and they are brought near enough together to discharge 
the jar, a spark will readily pass through the cardboard, 
leaving a clean hole behind it. Sheet after sheet may be 
added and readily pierced in this way, until the discharge 
capacity of the jar is reached. 

If the jar is a large one and well charged, the sparks will 
pierce a heavy fold of paper, sizeable books, and even sheets 
of glass. 

Peculiarities of the Static Discharge 

It will be noted that when a small book, or a number of 
sheets of thin paper, are held between the discharger-knobs 

60 



FURTHER EXPERIMENTS 

and a spark sent through them there is a burr on both 
sides of the book. If a rifle-bullet passed through the book 
from left to right, it is perfectly obvious that it would push 
the torn ends of the paper before it, and leave but one burr, 
and that on the right side of the book. But if the electric 
discharge is sent through the book in the same direction, 
from left to right, it will leave a burr of torn paper on both 
sides. This would seem to prove that there is a double 
discharge between the two points; a discharge from the 
positive side to the negative^ and one from the negative to the 
positive, either at the same time or immediately afterward. 
Possibly the discharge is a series of flashes back and forth. 



Further Experiments 

An illuminated electric sign can be made by pasting a 
continuous strip of tin-foil on a sheet of window-glass and 





1 ^ .. . — ^ V 'Hill 1 


c 


— ^-\- 


^-^r-f — Y-^ 






1 — — 1 








c 




: ^_^ 


r" 


- — 


-- ,, ' 


L_ 


1 ^ '-- ^ ^ -" ■ A 



Fig, 4 

cutting the strip with a knife to form the letters. The man- 
ner of making this strip is best shown by a picture (Fig. 4). 
In flowing along the tin-foil conductor the electricity has 
to jump across the knife slits, which causes a series of bril- 
liant sparks. As the knife slits are made in the form of 
letters or figures, the accompanying glow will always cor- 
respond. This experiment must be performed in the dark 
to be successful. 

61 



HARPER'S BEGINNING ELECTRICITY 

Another amusing experiment is to mount a doll's head on 
a stick of seahng-wax, or any other good insulator, and 
supply it with a head of real hair. This is done by selecting 
long hairs and sticking them in place. When this head is 
connected to the static machine by a concealed wire every 
hair will stand upright. A great deal of fun can be had 
with this toy. 

Perhaps the most interesting experiments of all can be 






Fig, 5 

performed with the aid of glass vacuum tubes, called Geiss- 
ler tubes. These cannot be made by the ordinary experi- 
menter without the assistance of an air pump, but they can 
be purchased at little cost. When these tubes are brought 
into contact with the static machine they produce strange 
light effects. The illumination varies with the speed of the 
machine, now flaming in violets and reds, now glowing with 
a soft mellow light. These tubes are made in a great 
variety of shapes and in all sizes. 

It seems that the air loses its non-conducting properties 
as it becomes rarefied up to a certain point. In the Geiss- 
ler tube the air is almost all exhausted. A bit of platinum 
wire at each end of the tube conducts the electricity to the 
inside, where it easily leaps across the long air-space, pro- 
ducing a bright light. 

Experiments with conductors are always interesting. By 
suspending wires or wet strings on glass bottles the current 
can be carried over long distances. It must be remembered 
that such lines are well insulated by the surrounding atmos- 

62 



FURTHER EXPERIMENTS 



phere, but they must be protected at all points of contact, 
else the electricity will escape back to earth. Outdoor 
transmission wires are suspended from wooden posts, and 
further protected at contact points by glass or porcelain 
insulators. Glass bottles will answer very well for indoor 
work. The wire can be held in a split cork protruding from 
the bottle mouth (Fig. 5). 

The transmission of electricity offers great inducement 
to those who like to play jokes on others. It is easy enough 
to arrange things so that grandpa will receive a jolt when he 
picks up his metal tobacco box, but such jokes should never 
be attempted. While they might or might not get the 
operator into trouble, there is even greater danger that the 
surprise and shock might injure an aged person. Of course, 
if the}^ knew they were going to receive a charge of elec- 
tricity, and were prepared for it, a heavy jolt might not hurt 
them a bit; but an unexpected charge is always dangerous, 
however slight, and should never 
be attempted with any person. 
Like all practical jokes, those 
emanating from electricity are 
always dangerous. 

Automatic electric chimes can 
be made by mounting three 
small bells on a metal rod. 
This rod should be about a foot 
long and provided with a ring, 
so it can be suspended while 
connected to the collector of the 
static machine, or the positive 

knob of th^ Leyden jar. The bells are mounted an 
equal distance apart on the rod. The two outer bells are 
suspended from small chains or wires. The center bell is 

63 



6 



HARPER'S BEGINNING ELECTRICITY 



I 



suspended by a silk cord, and connected to the ground with 
a chain or wire. Two metal balls are suspended from silk 
threads, so as to hang on either side of the center bell, with 
a bell on the outside of each (Fig. 6). 

When the chimes are connected to the generator the in- 
sulated metal balls are attracted toward the two outer 
bells, which are charged with electricity. As soon as the 
balls touch they are electrified, and are instantly repelled 
with considerable force. Touching the center chime, they 
are immediately discharged, only to be again attracted and 
discharged as long as the machine is in operation. If at- 
tached to the Leyden jar they will operate until it is dis- 
charged. 

Plenty of amusement can be had by arranging various 
little pieces of tin-foil on the outside of a long glass tube. 
These pieces can be arranged in any design, with a slight 
air-gap between each piece, and pasted firmly in place. 
When the end pieces are connected to the poles of the static 
generator the design will be repeated in brilliant sparks. 
This can also be accomplished b}^ using a glass plate instead 
of a tube. A fairly good electric sign can be made in this 
way (Fig. 7). 

If two metal disks be arranged on an insulated stand so 
that one is suspended over the other at a height of about 
five inches, then connected to the opposite poles of the ma- 
chine, httle pith images placed on the lower plate will im- 
mediately begin to dance up and down in a surprising [ 
manner between the two plates. This is caused by the at- 
traction and repulsion of the plates. The pith figures can 
be whittled into shape with a sharp knife. With a little 
glue very quaint dancers can be arranged (Fig. 8). 

The heavy current from the Leyden jar will heat and |„ 
melt fine metal wires. Adjust short pieces of fine wire 

64 



FURTHER EXPERIMENTS 



between the knobs of the fixed discharger and send the charge 
from the Leyden jars through the wire. Experiment with 
lead wires first. It will be noted that they can be easily 
melted into globules. It will require a heavier charge to 
melt an iron wire, and a still heavier charge to melt a cop- 
per wire. The finer the wires the easier they are heated to 
the melting-point. If two rubber-insulated copper wires 
are submerged in a glass tumbler and bent so their bare 
points are very near each other, water can be decomposed 
with a static discharge. When the charge leaps across the 
space between the insulated wires it will cause a series of 



^ 



^ 



Fig. 7 




Fig. 8 



bubbles to rise to the surface of the water. These bubbles 
are the hydrogen and oxygen gases which have been separated 
by the force of the electrical discharge. In this case the 
electricity exerts force enough to break apart the oxygen 
and hydrogen atoms which unite to compose the molecules 
of water. 

Only a few of the best experiments possible with a static 
generator are described here. Any one with a little imagi- 
nation and ingenuity can easily think of endless amusing 
and instructive experiments with static electricity. 

6s 



HARPER'S BEGINNING ELECTRICITY 

Do not attempt to run toy motors, railways, telegraphs, 
telephones, or to light miniature lamps with static elec- 
tricity. You certainly cannot operate such toys with this 
kind of electricit}^, and beyond a doubt you will ruin them 
if you make the attempt. The high potential or voltage of 
the static current will burn up and destroy all devices not 
made to withstand such a heavy discharge. 



Chapter VIII 

GALVANIC ELECTRICITY 

ELECTRICITY can be generated by chemical action. 
Nearly all chemical action produces some electrical 
energy. Only a few substances produce enough current 
during the chemical changes to warrant their being used in 
commercial work. 

A chemical electrical generator is known as a battery, and 
a single unit is a cell. 

A battery which produces electrical energy is designated 
as a primary battery. A battery for the storage of electrical 
energy is a secondary battery. 

An electric battery consists of three essential parts. 
There are, as in all electrical work, two poles to every bat- 
tery. These poles, or plates, are called electrodes or *' elec- 
tric roads." The positive pole, called the anode, from the 
Greek, meaning "way into," is usually of zinc. The nega- 
tive pole, called the cathode, also from the Greek, meaning 
"way up or out," is usually of copper or carbon. The third 
essential is the chemical solution, or electrolyte, usually of 
diluted acid, in which these plates are submerged. 

There are many variations of the electric battery. Dif- 
ferent metals can be used, different chemical solutions may 
be employed — the result is about the same. 

The electricity resulting from chemical action on the 
battery plates is called electromotive force. For convenience' 
sake this is generally abbreviated to the letters E. M. F. The 
5 ^7 



HARPER'S BEGINNING ELECTRICITY 

amount of E. M. F. in a battery depends upon the kind of 
plates used, the chemicals employed, etc. The more E. M. 
F. 2i battery can give the more power it has to force elec- 
tricity over the wires of a circuit. Electromotive force means 
practically the same as potential and voltage. 

A battery in which a hquid chemical is used is called a 
wet battery. Where a chemical paste is used in place of the 
liquid it is known as a dry battery. As a matter of fact, the 
dry battery is not dry at all. If it was it would not work. 
It is merely dryer than the wet battery. 

The E. M. F. of a cell does not depend upon the size of 
the plates used. The size of the plates determines the vol- 
ume of the current, not its voltage, or pressure. A battery 
made in a nut-shell will give just the same voltage, or press- 
ure, as one of the same kind made in a tub. The amount of 
current produced will be less, but the voltage will be the same. 

Electricity from the static generator is always small in quan- 
tity but high in voltage. Electricity produced by a chemical I, 
generator, or battery cell, is always very low in pressure or 
potential, and correspondingly high in quantity. Such bat- 
teries have a voltage of only one to two and one-half volts, 
or even less. 

The Wet Battery 



\ 



When two metal plates, one of zinc and the other of cop- 
per, are placed in an acid solution and connected by an 
electric wire they constitute a battery cell, and produce elec- 
tricity by chemical action. 

All of this chemical energy is not transformed into elec- 
trical energy. Some of it is wasted in heat-energy, some 
in the various chemical changes, and some is undoubtedly;, 
lost in other waj^s. 

If the copper and zinc plates are not connected by a wire| 

68 



GALVANIC ELECTRICITY 



■ or otherwise, no noticeable chemical action will take place. 
j When the plates are connected the electrical circuit is com- 
pleted and the action begins. As soon as the chemical 
! action starts the copper plate assumes a frosted, silvery 
I appearance. This soon develops into myriads of tiny bub- 
I bles. The bubbles unite and grow until they are buoyant 
I enough to rise to the surface, where they burst and their 
i contents escape into the air. These bubbles are caused by 
I the electrical decomposition, or breaking up of the water. 
: Water is composed of two parts of hydrogen gas to one part 
of oxygen gas. These two elements are separated by the 
passage of the electrical current. The hydrogen attaches 
itself to the copper plate until it escapes. The oxygen goes 
! to the zinc plate, forming zinc oxide. This hydrogen gas 
! would finally cover the copper to such an extent that it 
would resist the chemical action, and then the battery would 
cease to produce electricity. The copper in such a battery 
will remain unchanged for a long, long time, but the zinc 
will be slowly eaten away until the battery ceases to work. 

A Battery Defect 

When the copper plate is entirely covered with a protecting 
film of hydrogen it is said to be polarized. This means that 
there are counter-currents within the cell, caused by the 
hydrogen, which counteract each other and gradually de- 
crease the strength of the battery until it ceases to produce. 
A great many devices have been invented to keep the cop- 
j per plate free from hydrogen until the zinc plate is all con- 
] sumed. Some of the first batteries were made so the plates 
j could be moved about to obviate this nuisance. In others 
I chemicals were placed to neutralize the hydrogen. In dry 
batteries this latter practice is followed to-day — the carbon 

69 



HARPER'S BEGINNING ELECTRICITY 



'i 



rod, which is used in place of copper, is surrounded with a 
chemical which destroys the hydrogen, thus keeping the 
plate clear. In another type of battery it is kept from 
polarizing by the force of gravity. 

The action of the electric current in a battery is always 
the same as elsewhere. The current always flows from a 
higher to a lower potential. The action of the chemicals V 
on the metals maintains the higher potential in the battery 
so the current flows steadily over the circuit so long as this 
chemical action takes place. 



Explaining the Action of a Battery 



The action of a simple copper and zinc battery cell, with 
a diluted acid solution, is best shown in the following dia-;^ 
gram: 



© 



t 



COPPER 



e 




I 



Fig.t 



It will be noted by this diagram that the zinc plate, or 
anode, is the positive element of the battery, and that the 
copper plate is the negative element. The positive plate 
maintains the high potential which flows through the electro- 
lyte, or acid solution, to the negative plate. To complete its 
circuit the current must flow up and out of the top of the 
copper plate and along the wires to the zinc plate. Thus 

70 



GALVANIC ELECTRICITY 

it is that the negative plate produces a flow of positive elec- 
tricity, and is called the positive pole of the battery cell. As 
the electric current flows down the wire and into the zinc 
this is called the negative pole of the battery. 

When a wire connects the positive and the negative poles 
of such a battery it is called an electric circuit. It does not 
make any diff'erence how short or how long this wire is. 

Batteries for Open and Closed Circuits 

When the plates remain connected as long as the battery 
is in use it is called a closed-circuit battery. This type of 
battery is used for telegraph-Knes, etc. When the plates 
are connected only when in actual service it is called an 
open-circuit battery. A diff'erent type of battery is used for 
open- circuit work than for closed -circuit service. Open- 
circuit batteries are usually employed for rural telephone- 
lines, electric bells and buzzers, etc., where an intermittent 
current is required. 

Ordinary home-made batteries are short-lived at best. 
Their usefulness is hampered by many internal ailments. 
Common zinc generally contains bits of carbon and other 
metals which tend to produce local currents, or currents 
within the zinc itself, which quickly destroy it, even if 
the line circuit is broken. To prevent this the zinc surface is 
usually amalgamated by rubbing it with mercury. The 
copper plate quickly becomes coated with hydrogen. As 
soon as this takes place the copper plate is said to be polarized, 
and, of course, the chemical action stops at once. When 
the chemical action ceases the electric current will not flow. 
This will account for many apparent failures with home- 
made batteries. 

It cannot be shown that galvanic electricity differs materi- 

71 



HARPER'S BEGINNING ELECTRICITY 



In -:-'-- [ 



dynamo. It is only for the sake of convenience that it is 
designated as a separate kind. Zinc :nd copper are both 



in appearance and 

ames. It would be very 

hat zinc is, or copper 

:d as trying to describe 



metals, although they differ 
otherwise, and go by differ 
hard, indeed, for any one : 
either. It would be almost 
electricity. 

The potential difference in a battery cell is maintained be- 
tween the metal plates by the exc inn,: houid. When two 
plates of the same metal are in n r: fi in the chemical 
solution there will be no current In :n s case the chemical 
action is the same on both plates, and there can be no 
potential difference. The metals are said to neutralize each 
other. 

E. M. F. of Various Batteries 



A! 



coverea wiai a nqu a 
chemicals may be u_ r 
of some of the best-iin 



* ■ -^ - . - • - 


p(de 


1 Sil'-iiirn 


A>»epOjLdiriiziirig 
agent 


inYolts 


111-.: 


----- 


lilutedsol- 
pibiiric acid 


Potasaum 
Bidiroinate 


2.1 - 


Zinc 


Coppo- 


Blue vitriol 


None 


1.8 


Zinc 


Mercury 


Zinc sul- 
phate 


Mctcutous 
sulphate 


1.4 


Zinc 


Silva- 


Solution of 


None 


-65 



72 



GALVANIC ELECTRICITY 

A good battery should produce nearly two volts of electro- 

i motive force. Its internal resistance should be small. It 

should give a constant flow of current and be free from the 

evils of polarization. Above all it should be cheap, durable, 

and easily managed. 

No single battery cell is suitable for all purposes. Bat- 
teries must be selected for the work in hand. For telegraph- 
lines, etc., the closed-circuit batteries are generally used. 
For electric bells, telephones, ignition, etc., where a current 
must not flow except when the line is closed for service the 
open-circuit battery is necessary. 

Difference Between Primary and Storage Batteries 

Primary batteries, for producing current, should never be 
confused with secondary or storage batteries. A battery for 
storing electricity is an entirely diflPerent proposition. A 
storage battery will not give out electricity unless electricity 
is first put into it. It stores up the electrical energy in the 
form of chemical energy. When drawn upon it will reverse 
this operation and change the chemical energy back into 
electricity — with a slight loss in heat, etc. 

The secondary battery, or accumulator, is a cell in which 
a certain chemical action is first produced by electricity. 
This process of storing up electrical energy into chemicals 
is called charging. When the battery is producing current 
It is said to be discharging. 

The common storage battery is made of plates immersed 
j in an electrolyte. The anode plate is made of spongy metallic 
I lead, and the cathode plate of lead peroxide. These active 
i elements of the battery cell are both changed into lead sul- 
I phate when the battery is discharged. Charging the battery 
changes them back again into spongy lead and lead peroxide. 



Chapter IX 

BATTERIES AND HOW TO MAKE THEM 

VOLTA made the first successful electric battery in 
1789. Since that day, more than a hundred years 
ago, the electric battery has been steadily improved. 

If a bit of blotting-paper is moistened with salt water 
and placed on a copper cent, and then covered with a silver 
dime, it will produce a very little electricity when the cop- 
per and silver are connected with a piece of wire. It is such 
a little current that it will require a delicate instrument to 
register it. Touch the tongue to the ends of the connecting 
wires, and a pecuKar taste can be detected. This "taste" 
is caused by the action of the current on the nerves of the 
tongue. 

Volta's first electric battery was something like this 
penny-and-dime affair. He cut a number of circular disks 
of metal and arranged them in a stack, each pair separated 
by paper moistened in salt water, which he called a galvanic 
pile. It is easy enough to make such a "pile." Cut a 
dozen pieces of sheet zinc and an equal number from sheet 
copper three inches square, cut twenty-four pieces of cloth 
the same size, and soak them in very salty water. Begin 
the "pile" with a square of zinc, then lay on a piece of the 
wet cloth, followed with a piece of copper. Lay the metal 
disks and the cloth evenly until the pieces are all in place, 
taking care that the same order — zinc first, cloth next, and 

74 



HOW TO MAKE BATTERIES 

copper last — is maintained throughout. The pile should end 
with a copper disk. 

The voltaic pile made in this way will not produce cur- 
rent until the circuit is complete. Connect the bottom zinc 
to one terminal wire and the top copper disk to the other. 
Whenever these two terminals are brought together the 
current will flow (Fig. i). 

A Simple Battery 



Another experimental battery can be made by submerg- 
ing a zinc and a copper plate in a common glass tumbler 
filled with salty water. The metal plates should be about 




Fig. t 

two inches wide and long enough to extend well above the 
glass, where they are bent sharply back against the rim to 
keep them in an upright position and well away from each 

75 



HARPER'S BEGINNING ELECTRICITY 

other. They must not touch each other, either on the in- 
side of the glass or on the outside. Before placing the metal 
plates in the glass punch a small hole in the top of each to 
admit the terminal wires (Fig. 2). 

These little batteries are for experimental purposes only. 
They produce very weak currents. The voltaic pile can be 
made large enough by adding a sufficient number of plates 
to produce a current which can be felt when the terminal 
wires are grasped in the hands. But it will require a very 
delicate instrument to detect the weak current of the tum- 
bler or coin battery. 

Detecting Weak Battery Currents 

The device used to note the presence of an electric cur- 
rent is called a detector. A very simple one can be easily 
made with a small pocket compass, costing but a few cents, 
and a short piece of fine insulated copper wire. Select a 
compass with as long a needle as possible. Wind twenty 
turns of fine insulated copper wire. No. 30, about the com- 
pass, from north to south, and fasten in place with a bit 
of thread. Leave the ends of the wire free for connection 
with the batteries to be tested (Fig. 3). 

The common name for this instrument is a detector, but 
electricians speak of it as the galvanoscope. It will detect 
the presence of very weak currents. In order to use it the 
terminal wires are connected to the battery wires so the 
current will flow through the insulated wire wrapped around 
the compass. It was nearly a hundred years ago that Hans 
Christian Oersted, of Copenhagen, discovered that the 
compass needle was deflected when brought near and parallel 
with a wire carrying an electric current. The galvanoscope 
is an adaptation of this very principle. 

76 



HOW TO MAKE BATTERIES 

To use the detector mount it on a wooden base so the wires 
will not become disarranged. The compass can be simply 
glued in place, fastened with a bit of hot sealing-wax, or 
fitted in a shallow hole. Scrape away the insulation from 




Fig. 2 




Fig, 4 

the ends of the terminal wires for about an inch until the 
metal is bright and clean. Fasten these ends to two brass 
tacks driven into the wooden base. Twist the wires firmly 
about the tacks. 

Ordinarily the compass needle will point north and south. 
This is also the direction of the coils of wire on the com- 
pass. Attach the terminals of the^battery to be tested to the 
terminals of the instrument (Fig. 4). If a current is flowing 
through the wire the needle will be deflected according to 

77 



HARPER'S BEGINNING ELECTRICITY 

Oersted's law. It will swing to the right, or to the left, 
according to the direction of the flow. The degree of de- 
flection will always depend upon the strength of the current. 

The Galvanometer 

A very sensitive galvanometer can be made by suspending 
a magnetized needle in the center of a coil of insulated wire. 
The needle should be balanced on a fine silk fiber — the finer 
the better — and suspended in the upright coil so that it 
points toward the wire (Fig. 5). 

When a weak current of electricity is sent through the 
coil its magnetic influence ox field of force aff'ects the needle. 
According to one of Oersted's laws, the needle will im- 
mediately swing around and point at right angles to the 
wires, or east and west, instead of north and south. 

Another type o^ galvanometer is made of a flat coil of fine 




Fig, 5 Fig, 6 

silk-covered wire wound on a flat spool, and adjusted so 
that a good pocket compass can be set securely on the top 
of the wire. This coil must be placed so that the parallel 
wires run north and south. In other words, the needle when 
at rest must be parallel with the insulated wires on the 
coil (Fig. 6). 

78 



HOW TO MAKE BATTERIES 

Care should be taken to have the compass needle exactly 
parallel with the wires beneath the compass. The terminals 
of the wire coil are brought to the top of the spool for con- 
venience in making connections with the electric circuit. 
When a current is sent through this coil the magnetic needle 
will be deflected until it stands at right angles to the wire. 
If the connections are reversed, and the current sent through 
from the opposite direction, the needle will again swing 
to right angles with the wires, but it will turn the other 
way. 

Very weak currents can be measured with this galvanom- 
eter, because the insulated coils of wire multiply the force 
of the electric current. 

An Experimental Battery 



A very good experimental battery can be made in a large 
soup plate, or any other shallow earthenware dish. Cut 
out a circular disk of zinc a Httle smaller than the bottom 
of the dish. This metal disk should have an "ear" on one 
side so it can be bent up at right angles for the wire connec- 
tions. This zinc disk should 
be covered with a sheet of 
blotting-paper and laid in the 
bottom of the dish. Cut a 
second disk of sheet copper, 
with an "ear" to stick above 
the dish, and lay it on top 
of the paper. Care should 
be taken that the two metals 
do not touch at any point. A short piece of copper wire 
should be twisted through holes punched in the "ears," 
after the parts have been scraped clean with a knife. Make 

79 




Fig, 7 



HARPER'S BEGINNING ELECTRICITY 

a good joint, and see that the metals are bright at the points 
of contact. 

The dish should be filled with a strong solution of blue 
vitriol, diluted nitric acid, even plain salt and water. As 
blue vitriol and diluted acid are a poison, they should always 
be handled with extreme care. Do not get too much of 
either on the hands, and be careful to keep such chemicals 
out of cuts and bruises (Fig. 7). 

To operate this battery the ends of the wires should be 
brought together for a few minutes, then it is ready for use. 
The zinc will be dissolved after a little and will have to be 
replaced. Every now and then the copper disk must be 
taken out and scraped, or sand-papered, to remove the 
polarizing hydrogen. 

A Good Wet Battery 

A more powerful battery of this same nature can be made 
by using a glass jar and larger pieces of zinc and copper. 
The copper is cut in a strip, coiled in a spiral, and placed 
in the bottom of the jar. The wire connecting to the cop- 
per coil and extending out of the jar must be covered with 
a rubber insulation. Near the top of the battery is sus- 
pended a zinc casting, usually in the form of a "crow's foot." 
A number of zinc strips firmly riveted together can be used. 
The jar is filled with water, in which is thrown a small 
quantity of blue vitriol, to a point just submerging the zinc. 
The circuit should be closed for a few hours by connecting 
the lead wires, and it is ready for use. 

In Fig. 8 are shown different types of wet batteries: the 
carbon and zinc rod cell (A); two-fluid cell (B); gravity 
cell (C). 

Blue -vitriol batteries are all right where only a little 

80 



HOW TO MAKE BATTERIES 

current is required for contniuous service, such as in tele- 
graphing. They are called gravity batteries because the 






Fig. 8 

plates are kept from polarizing by the force of gravity, 
which keeps the copper sulphate at the bottom of the jar 
and the zinc sulphate at the top of the jar. 



The Dry Battery 

Where a larger current is required for short intervals the 
dry battery is best. Dry batteries can be purchased for 
about twenty-five cents each, or less, and at this price no 
attempt should be made to construct them. The principles 
are the same as those of the gravity battery, and a brief 
description of a dry battery will be quite sufficient. 

As noted before, the dry battery is not "dry" at all. 
The chemical solution is applied in the form of a paste in- 

8i 



HARPER'S BEGINNING ELECTRICITY 

stead of a liquid. The present type of dry battery consists 
of a zinc cup, or container, which is the negative pole. A 
positive pole, consisting of a rod of carbon, is surrounded by 
a mixture of manganese dioxide, ground carbon, and elec- 
trolj-te. The zinc cup is rolled from thin zinc; the paper 
partition consists of a single layer of heavy pulp-board; 
the positive-pole mixture consists of 85 per cent, manganese 
dioxide, 100 parts by weight; ground coke, 80 parts; arti- 
ficial graphite, 20 parts; sal-ammoniac, 20 parts, and zinc 
chloride, 7 parts. The manganese dioxide acts as the 
depolarizer; the ground carbon, which is next to the paper 
separator, collects the current and conducts it to the center 
carbon plug; the graphite is employed to reduce the in- 
ternal resistance; the sal-ammoniac is the electrolyte, while 
the zinc chloride is used only to improve the hfe of the cell 
by reducing local action. 

A Carbon-Zinc Battery 

To make a good carbon-zinc battery secure a large glass 
jar holding about two quarts. The other materials neces- 
sary are a small rod of zinc, a piece of electric-light carbon 
such as the arc-lamp "trimmers" throw away, two circular 
pieces of wood about three inches in diameter and one-half 
inch thick, some fine powdered coke, and a piece of flannel 
cloth. 

A hole must be bored in the center of the wooden disks 
to admit the carbon rod; the flannel is fastened to these 
disks with string to form a tube or bag. This bag is filled 
with the powdered coke packed tightly about the carbon rod. 

The zinc rod and the carbon rod are suspended upright 
from the top of the jar by means of a wooden cover. They 
are insulated from the wood by porcelain or glass receptacles, 

82 



I 



HOW TO MAKE BATTERIES 

or insulators. The conducting wires are adjusted from the 
zinc and copper rods respectively (Fig. 9). 

When this jar is filled about two-thirds full of sal-am- 
moniac solution, using one and one-third ounces of the 
chemical to each quart of water, the battery is ready. 

Care must be taken in operating this battery, and all 
other carbon batteries, including dry batteries, not to leave 
the wires connected for any length of time, as they will soon 
cease to produce electricity if short-circuited in this way. 



CARBON-Jll 




-ZINC 






l\ 












xL L 








WOOD 




^ ^ 














\- 


wu \ 




= ^J 


^l Ay^ •i.yj. 






r^^' 


•,y. ^vN _~-"L" 


r*.jr^i^ 






;..V Vk -— .— 






ZJI1 




— — > 




zzr 


it *»" » *?^ ^t —'—- 


r-_-_-- • 




•— _ 


:;*:• ''S*' nr"""' 


-— — — ; 


\.ir\r\r\- 


-— 


m UT^- 


I- _T j 


WOUD 


r^^l^^^sm^^ 




Fig. to 



Fig. 9 



In operating this type of battery a spring connector is 
always best. This spring opens the circuit when the battery 
is not in actual use. A common "push-button" will answer 
this purpose very well. A good connector can be made with 
two strips of brass screwed to a bit of board (Fig. 10). 

A bit of sealing-wax on top of the spring will serve to 
insulate the finger from the brass. 

Battery Currents Weak and Harmless 



All batteries are perfectly harmless. The voltage is very 
low, and it is quite impossible to get a noticeable "shock" 
6 83 



HARPER'S BEGINNING ELECTRICITY 

from a single battery cell. They give a potential of but 
two volts at the most, and this cannot be felt when the ter- 
minal wires are held in the hands. 

Of course two volts is not enough pressure to force elec- 
tricity over an}^ great distance of wire. Where long circuits 




Fig.U 




Fig. 12 




Fig. IS 

are used a number of batteries must be coupled together to 
raise the voltage, or pressure, for it must overcome the 
natural resistance of the wire. 

It is obvious that if one battery will give two volts, two 
batteries will give four volts, and so on indefinitely. Davy 
used a battery of two thousand cells to secure a high- 
voltage current. 

84 



HOW TO MAKE BATTERIES 



To connect a number of batteries in series in this way, in 
order to raise the voltage, the positive pole of the first bat- 
tery should always be connected to the negative pole of the 
next battery. This should be repeated until all the bat- 
teries are connected. When all are united the series should 
begin with a positive wire and end with a negative, or vice 
versa. Fig. ii shows a battery of five cells connected in 
series. Connected in this way they will give about twenty 
amperes at seven volts. 

To connect the batteries in multiple, so as to secure a 
heavy flow of current at low pressure, as is sometimes neces- 
sary, all the positive plates should be connected together 
and all the negative plates united. 

It is also possible to combine both series and multiple 
and connect up the batteries so as 
to secure a good flow of current at 
a reasonable voltage (Fig. 12, 13). 

It is always cheaper and better 
to purchase electric batteries for 
experimental work than it is to 
make them. Batteries of all 
kinds can be purchased at a very 
low and reasonable price. But 
if one desires to understand the 
principles of a battery, to know 
all about such electrical currents, 
it is best to make the small ex- 
perimental batteries. Experi- 
ence is always the best teacher — 
if the most expensive. 

Almost every automobile garage has on hand plenty of 
dry-cell batteries which are "worn out" for ignition pur- 
poses, They can be bought for a few cents each, and often 

85 




Fiff. U 



HARPER'S BEGINNING ELECTRICITY 

the owner will be willing to give them away. While these 
cells will not produce enough electricity to operate the 
"spark" in a gasolene-engine, they are far from being worn 
out. Often these cells are only polarized, and will be almost 
as good as new after a short rest. If twelve of them be 
secured, and thoroughly warmed near the stove, they can 
be connected up so as to give a very good current. 

Arrange the cells in four rows of three each. Connect as 
shown in Fig. 14. 

With this combination the cells will give three times the 
current strength of a single cell, and four times the voltage. 



Chapter X 

EXPERIMENTS WITH BATTERY CURRENTS 

IT will be instantly noted that the battery current flows 
in a steady stream over the wires. UnHke the static 
current, it causes no brilliant flashes of flame, no crackling 
sparks. Only with a number of strong batteries, in series, 
can a very tin)^ bluish spark be secured. It would require 
a battery of nearly fifteen thousand cells to produce a po- 
tential sufficient to force the current over one inch of air- 
gap. 

The static current is comparable to a very thin spurt of 
water under high pressure, and the battery current to a 
heavy stream of water under very little pressure. The 
behavior of the static current is also very much diff'erent. 
It seems to collect on surfaces — to flow in spurts — even to 
stand still. Galvanic electricity flows steadily along its 
course. It does not seem to collect on anything. 

Battery Currents Are of Low Voltage 

Many substances which are fairly good conductors of 
high-voltage static electricity are non-conductors, or in- 
sulators, of weak battery currents. Dry wood will not 
entirely resist the flow of static electricity, but it will answer 
very well as an insulator of low-voltage battery currents. 

Batteries seldom exceed a potential of two volts, generally 

87 



HARPER'S BEGINNING ELECTRICITY 

they are nearer one volt. For this reason it is essential that 
all connections be made as good as possible. The slightest 
air-gap, a bit of dirt, or an oxidized scale on the wire is quite 
sufficient to stop the flow of such weak currents. In join- 
ing bits of wire, connecting wires to battery terminals, 
lamps, etc., be sure that all the insulation is scraped away. 
Scrape or file the metal until it is clean and bright. Always 
twist the wires firmly together. When making a wire con- 
nection take a number of turns and twist tight with a pair 
of small pliers or pinchers. 

Wire Circuits for Battery Currents 

It is best to clean and solder all joints, but, of course, 
this can only be done where the work is of a permanent 
nature. Copper and most other base metals oxidize 
rapidly in the air and soon become covered with a film of 
insulation. This must he scraped of before a good connection 
can he made. 

Where wires have to be connected and disconnected very 
frequently in conducting experiments small wire clips can 
be used to advantage. These clips are used to slip over 
the edge of loose sheets of paper to hold them together. 
They are always bright and clean, being "washed" with tin 
or nickel, which does not oxidize rapidly. If such a clip 
is firmly spliced or soldered to the end of the wire leading 
from each battery terminal it will save a great deal of time 
and inconvenience, and at the same time it will always make 
a good connection (Fig. i). 

A lesson in bending, twisting, and connecting wires may 
not be out of place. This lesson is best told in a series of 
pictures. 

In splicing, or connecting, two bare wires take at least 



BATTERY CURRENTS 

four turns for the neck and five at each end. This will 
make the sphce as strong as the wire (Fig. 2). 

In tapping an insulated main-wire the insulation is first 
cut away for a small two-inch space. The tap-wire is given 
four turns in the neck. Wind with insulation tape (Fig. 3). 



A 




Hi, , 



B Turns 3 



4 i\ 1 



^^fflSfesssss^^ffl^ 



■Utifwistecl Sleeve 
Sleeve- 




Fig. 2 



U 

Fig 4. illustrates sphcing insulated wires; Fig. 5, tapping 
and splicing; and in Fig. 6 are shown taps and splices in 
standard wires. 

Experimenting with a Battery 



With a galvanoscope to detect the presence of an electri- 
cal current in any conductor, the first experiment should be 
with various metal plates in the primary battery. After 
noting the deflection of the detector needle when the 
zinc and copper plates are immersed in the sulphide, or 
acid solution, take out the zinc plate and insert a sheet of 
lead. Change the lead to tin, to iron, to brass, to aluminum, 
etc., and note the results. The battery should also be tried 
out with various combinations of metal plates, such as lead 

89 




Binding Wire 




•Main Vfire 



Fig. 2 



Tap Yfire- 



Ruhber Tape 




yL-sp':^tK-;r 



Rubber Taps- 



-plefed Splice 



Sc'.der Tiere- 




Fig. 4 



■Wea'-'-e'-c-^-- 



.'Main Wire 



-Tap VHre 



-Tape Sleeyina 



Si^^f^A - Coppfr Sleeve ^ _ B_ 



S^-a'd-. 



■Conductor 



Fig. 5 




■ Insuldtfon 



.'Insulation Insulation-.. 

iL.'^:,^.^,::.-^^..--..,. : : -^'i "*>i :;^T^.S-s:-sjf Tap, 

''Stranded Conductor Conductor 





Fig, 6 

TAPPING AND SPLICING INSULATED WIRES 



BATTERY CURRENTS 

and brass, aluminum and iron, zinc and carbon, and the re- 
sults noted. Different battery solutions can also be used, 
including salt water, a solution of common vinegar, sal- 
ammoniac, etc. 

It will be found that nearly all the metals will give some 
electricity, although the quantity will be small for the most 
part. Zinc and copper or zinc and carbon will give the 
best results. 

The galvanoscope will also show the direction of an elec- 
tric current. When the battery current is sent through the 
wire coils of the instrument in one way the needle is de- 
flected. By reversing the wires at the terminals the needle 
will quickly swing an equal distance to the other way. 
This proves beyond a doubt that the direction of the flow 
has been changed. 

It has been said that the size of the battery has nothing 
to do with the potential or voltage of that particular kind of 
a battery. This can be easily proven with the aid of the 
galvanoscope. Construct a common zinc and copper cell 
in a small tumbler. Cut the plates two inches wide and 
four inches long. Arrange it so the zinc and copper 
plates stand upright in the tumbler without touching. Fill 
the tumbler nearly full of strong salt-water solution and 
note the deflection of the needle in the galvanoscope, which 
indicates the strength of the current generated, and not its 
volume. Take out the plates and wipe them dry. Pour 
out enough of the acid solution so that the plates will be 
submerged only for about a quarter of an inch, and test the 
battery on the galvanoscope. 

It will be found that the deflection of the needle is the 
same in both cases, although the size of the plates in the 
solution varied from several square inches to less than one 
square inch. 

91 



HARPER'S BEGINNING ELECTRICITY 

Measuring Resistance 

By varying the distance between the two plates of any 
battery, and testing them with the galvanoscope, it will be 
noted that the distance separating the battery plates seri- 
ously affects the current strength. The battery liquids do 
not conduct the current as well as the metals. This is due 
to the internal resistance of the battery. The terminal 
wires, instruments, etc., of the circuit make up the external 
resistance of the circuit. 

With the aid of the detector the resistance of various 




CELL QALVANOSCOPE 



CELL 



^ IRON WIRE — > 

Fig.? 

materials may be tested by placing them in the battery 
circuit and noting the deflection of the magnetic needle in 
degrees before and after the test material is inserted in 
the Hne (Fig. 7). 

The unit of resistance is called the ohm. Dr. George S. 
Ohm, of Germany, worked out the law of electrical resist- 
ance. In his honor this unit is called an ohm. An ohm is 
the resistance offered by a column of mercury having a 
length of a little over three feet with a cross-section of one 
square millimeter. Nine feet and nine inches of No. 30 
copper wire or 39 feet i inch of No. 24 copper wire offer 
about one ohm of resistance. 

Coils of wire with the resistance determined by previous 

92 



BATTERY CURRENTS 

measurements are called resistance coils. To make a re- 
sistance coil the insulated wire is first doubled before it is 
wound on a spool, or in a coil, to neutralize the magnetic 
influence of the lines of force which surround every wire 
when electricity flows over it. 

Such coils can be easily made and tested on the galvano- 
scope. 

That the resistance of a wire is directly in proportion to 
its length can be easily proven by stretching a long wire 
back and forth on an insulated frame and testing it out at 
every turn with the galvanoscope (Fig. 8). 

Test the resistance from A to B, from A to C, and so on 
down to H, It will be found that the resistance increases 
in proportion with every added length of wire. 

An Explanation of Resistance 

Resistance corresponds to friction. That is, the friction 
inside an iron pipe retards the flow of water through the 
pipe. The pipe can be made so long that this friction will 
overcome the water pressure and the water will cease to 
flow. There may be a hundred pounds of water pressure 
to every square inch of pipe surface near the pump. This 
pressure grows less and less as the pipe extends, owing to 
the friction of the water against the pipe, until it vanishes 
entirely. 

It is the friction, or resistance, ofl"ered by the conductor 
to the current which cuts down the potential of an electric 
current. The current may leave the dynamo at a pressure 
of 1 20 volts. This voltage grows less and less as the wires 
extend until the flow ceases .entirely. 

A little experiment with a single battery cell and a gal- 
vanoscope will show that after the circuit wires reach a cer- 

93 



HARPER'S BEGINNING ELECTRICITY 

tain length the current ceases to flow. If another cell is 
connected up in series with the first cell the current will 
flow again. This is because the current now has twice the 
potential, and, therefore, will flow twice as far over the 
wires. 

How the Battery Current Travels 

It is hopeless to try to explain how electricity travels 
over a wire. As well try to tell how water travels through 
a pipe. In the case of water in a pipe, it travels easily 
through the air, or ether, and is surrounded with an impass- 
able barrier of metal. With electricity this is exactly re- 
versed. The current flows easily through the metal and is 
surrounded by an impassable barrier of air. It is about as 




120 V. 



xy 



— e 



Fig, 9 



Fig, 8 

difl&cult for electricity to flow through air as it is for water 
to flow through iron. Only by destroying the air with 
enormous pressure can electricity flow through it. Only by 
breaking the pipe with enormous pressure can water pene- 
trate iron. 



94 



BATTERY CURRENTS 

If the electric circuit be broken, the current ceases to 
flow, but the potential still exists in the wire. This is also 
analogous to water in a pipe. If the pipe is plugged the 
water ceases to flow, but the pressure still exists in all parts 
of the pipe. 

Electricity cannot flow over the wires A and B (Fig. 9), 
but the potential of 120 volts exists in A and B ready to flow 
on the instant the circuit is completed. The compass de- 
tector will show that this potential exists in the branch wires. 



Chapter XI 

ELECTRIC CIRCUIT 

THE study of the chemical battery invariably leads to 
the question of circuits. 

It has already been explained that a circuit is the path 
over which electricity travels from and to its source. 

When a lamp, motor, electric flatiron, or any other elec- 
trical device is connected to these wires it is said to be in 
circuit. 

When the electrical circuit, or path, is suddenly made 
shorter, through accident or design, it is said to be short- 
circuited. 

Electricity always travels over the shortest path. It 
cannot be sent over any line unless the conductors are all 
carefully insulated at all contact points to prevent the 
current from jumping off and cutting across between the 
positive and negative wires, or dashing to the ground and so 
back to its source. 

Electricity, for all its mighty energy, is not a willing 
worker. It is naturally and inherently lazy. It requires a 
great deal of energy to get it started at any task — actually 
more energy than it will produce in work. It will take ad- 
vantage of every chance to shirk. It will slip away at every 
opportunity to avoid work. 

A short circuit occurring between the transmission wires 
is said to be "shorted" across the line (Fig. i A). When it is 

96 



ELECTRIC CIRCUIT 



i short-circuited to the earth it is said to be *' grounded'' 
I (Fig. I B). 

When only a small part of the current is directed aside 
I over a branch path it is called a shunt circuit (Fig. 2). 
j When the wires are broken, or separated in any way so 
I as to disconnect them, the circuit is said to be open or 




=±. 



d 



Fig. / A 



Fig. 2 




Fig. t B 

broken. When the break is repaired, or the circuit closed 
by a switch, or other means, it is said to be closed or made. 
To fully understand this let us follow the flow of elec- 
tricity through an ordinary house circuit. 

The Electrical Path 

The current leaves the generator at the power-station in 
a steady flow and under considerable pressure. This cur- 
rent travels over an insulated wire out in the street at the 
rate of 186,000 miles a second. These wires, though of the 
best copper, off'er some resistance to the flow, and to over- 
come this resistance the electricity loses some of its voltage, 
or pressure. At every point where the wires are suspended 

97 



HARPER'S BEGINNING ELECTRICITY 

from the poles they must be insulated with heavy glass or 
porcelain insulators, or it would jump off and short circuit 
back to the power-house. The current enters the house 
over a copper wire carefully insulated with rubber and 
further protected with porcelain tubes where it goes through 
beams, walls, floors, etc. This wire leads it to the watt- 
hour meter, which determines how much electricity is being 
used. From the meter the current flows along a copper 
wire, hidden away in the walls of the house, to the electric- 
lamp fixture. Here it encounters an incandescent lamp, or 
even two or three lamps. The filament in the lamp is a 
very small tungsten wire, looped many times. This wire 
is no larger than a hair. It offsets considerable resistance 
to the passage of the current. But there is ample pressure, 
or voltage, to force the current through it. In overcoming 
this resistance the wire is made white hot. All substances 
emit light when brought to a white heat. With some of its 
voltage lost in overcoming the electricity in the lamp, or 
lamps, the current begins its return journey. Parallel with 
the wire which conducted it into the house and through 
the walls is another copper wire of the same size. This wire 
is placed about three inches from the other wire. It is 
also carefully insulated, because the current still contains 
considerable strength. The current leaves the house by 
this second wire, which also passes through the meter, and 
continues down the street over another wire back to its 
source in the power-house. 

Different Forms of Circuits 

There are a great variety of ways of forming electric cir- 
cuits. 

When a number of conductors are arranged so that the 

98 



ELECTRIC CIRCUIT 

current must travel over a single path, the conductors are 
said to be connected in series (Fig. 3). 

In this case it will be noted that the current has but one 
path over the wires and through the lamps from the positive 



) 



^ 



Fig. 3 

to the negative poles of the dynamo. The wire, and each 
individual lamp, offer some resistance to the passage of the 
current. The resistance to the passage of any electric cur- 
rent may be obtained by adding the resistances of the 
various conductors through which the given current passes. 
When the resistance is increased along the circuit it makes 
a difference in potential, or voltage. It is apparent that the 
resistance offered cuts down the voltage. But it must not 
be forgotten that, regardless of the voltage, the current is 
uniform throughout the series circuit. When the con- 
ductors are all in series there is but one path for the current, 
and there must be as much current at one end of the circuit 
as at the other. If this were not true there would be an 
accumulation of electricity at certain points along the cir- 
cuit. We know there is no such accumulation, therefore 
the flow of electricity is uniform throughout. To make this 
clear imagine the electricity to be water flowing through a 
pipe. If there is a certain quantity of water entering one 
end of the pipe, that same amount must be able to pass 
any section of the pipe, and the same quantity must flow 
out of the pipe in the same length of time. It is impos- 
7 99 



HARPER'S BEGINNING ELECTRICITY 

sible for water to accumulate in appreciable amounts in 
the pipe. 

Remember it is not the current in an electrical circuit 
which is used up. The energy of the electrical circuit only 
is utihzed. 

The circuit may be divided by grouping the conductors 
so that there are as many paths for the current as there 
are conductors. In this case the conductors are said to be 
in parallel, or multiple (Fig. 4). 

Incandescent lamps in the house are nearly always con- 
nected in viidtiple, or across the line. Arc-lamps for street 
illumination are usuall}' connected in series. 



$3 



Fig, 4 
I 



^ 



^ B 



Fig. 5 

It is easier for water to flow through a large pipe than it 
is for it to flow through a small pipe. It is easier for elec- 
tricity to flow over a large wire than it is for it to flow over 
a small wire. The detector will prove that doubhng the 
cross-section of a wire conductor reduces the resistance one- 
half, providing the wires are of the same length. 

The more paths for the electric current the less the 
resistance. 

If the wires i, 2, 3, 4 (Fig. 5) have the same resistance, an 

100 



ELECTRIC CIRCUIT 

equal amount of current will flow through each. The cur- 
rent will always follow the path of least resistance, and if 
No. 4 offers the least resistance the most of the current will 
flow through No. 4. 

The resistance of a coil of wire depends upon its tem- 
perature. To prove this test out a coil on the galvanoscope, 
noting the resistance. Then heat the wire on the stove and 
test it. 

As a summary of these tests it is shown that the resist- 
ance of a wire depends upon its length. That it also de- 
pends upon the diameter, or cross-section, of the wire and its 
temperature. 

Measuring Electricity 

It was while studying with similar battery circuits that 
Faraday, Ampere, Oersted, Ohm, Wheatstone, and others 
worked out the rules for measuring electricity. They also 
produced numerous instruments for this purpose. 

It is very easy to measure the resistance of a wire with the 
galvanoscope. By noting the deflection of the needle it 
will be seen that doubling the length of any wire also doubles 
its resistance. By comparing the flow of electricity to the 
flow of water in a pipe it is also easy to understand that the 
current loses some of its pressure in overcoming this re- 
sistance. 

We can also measure the current's strength, its quantity, 
and the amount of work it will do in a certain amount of 
time. 

The strength, or energy, of an electric current is measured 
by the amount of work it can do. This depends upon the 
rate of flow. 

Current strength is measured in amperes. A current 
having a strength of one ampere, it has been determined, 

lOI 



HARPER'S BEGINNING ELECTRICITY 

when passed through a solution of silver nitrate, will deposit 
6.001 1 88 grammes of silver in one second of time. All this 
is very technical for a beginner. Perhaps it is best to say 
that an ampere is equal to a current of one volt pushing its 
way through a resistance of one ohm. 

The amount of work a water-wheel will do depends upon 
the rate of flow of the water. This rate of flow in the 
water pipes is measured in cubic feet per second of time. 
It must be understood that amperes measure the rate of 
flow of the electric current. The quantity, or amount of 
current, is measured in coulombs. A coulomb is the amount 
of electricity given in one second by a current having a 
strength or rate of flow of one ampere. Coulombs are deter- 
mined by multiplying amperes by seconds. 

A current of six amperes will give sixty coulombs in ten 
seconds. 

6 amperes x lo seconds = 6o coulombs. 

The potential diff'erence which causes the flow of cur- 
rent is expressed in volts. It requires one volt of electro- 
motive force to send one ampere over one ohm of resistance. 
This will explain why the pressure, or potential, of a cur- 
rent is the same as voltage. If the potential diff'erence 
between two wires of a line is 120 volts the voltage of the line 
is 120 volts. 

The amount of work that an electric current will do is 
measured in watts, so named in honor of James Watt. A 
current of one ampere with an E. M. F. of one volt will do 
one watt of work. Seven hundred and forty-six (746) 
watts equal one mechanical horse-power. A thousand 
watts are called one kilowatt. 

Amperes x volts = watts. 
Watts -T- 746 = horse-power. 
102 



ELECTRIC CIRCUIT 

When James Watt first began to experiment with his 
steam-engines they were used to pump water from mines. 
He had no way of expressing the power of his steam-engines. 
Large draft-horses were used for this pumping-work before 
Watt invented the steam-engine. Whenever Watt installed 
a steam-engine he found that it displaced a certain number 
of these horses. This led him to express the energy of his 
engines in horse-power. To determine just what a horse- 
power was he experimented with the largest types of English 
draft-horses working in the London breweries, and found that 
a good horse would lift a weight of 33,000 pounds one foot 
in one minute of time. He adapted this as a basis for figur- 
ing the power of his engines. Later this was officially adopt- 
ed as the unit for computing the energy of all power ap- 
paratus. 

A delicate instrument called a voltmeter is used to measure 
the potential difference, or voltage, of a circuit. 

Meter is French for measure. 

Other instruments are used to determine the flow of cur- 
rent and the amount of work it will do. The ammeter is 
used to measure the amperes, and a wattmeter for ascertain- 
ing the watts, or the amount of energy consumed. 

These instruments are all very dehcate and hard to 
make. They are not at all necessary for the elementary 
study of electricity. They are required only for advanced 
work, and can be purchased much cheaper than they can 
be made. 

Transmitting Electrical Energy 

Line resistance is a very important study, and should 
not be neglected, as it has a direct bearing on nearly all 
electrical work. 

103 



HARPER'S BEGINNING ELECTRICITY 

Where the conductors are connected in multiple the total 
resistance of the circuit is not equal to the sum of the several 
resistances, as it was in the series circuit. The total resist- 
ance of eight incandescent lamps, each having a resistance 
of 220 ohms, connected in multiple across a no- volt cir- 
cuit, is zyyi ohms. The total resistance of the eight lamps 
is equal to the resistance of any one of them divided by the 
total number of lamps connected in multiple. 

220 ohms -7- 8 lamps 27^ ohms. 

To find the amount of current taken by these lamps divide 
the voltage by the resistance. 

no volts -^ 27^ ohms = 4 amperes. 

It is possible to divide the circuit into both series and 
parallel combinations. Lamps, or other electrical devices, 
can be connected so that some of them are in series and 
others are in multiple (Fig. 6). 




ELECTRIC CIRCUIT 

In certain kinds of electrical work it is far cheaper to 
utilize the earth as part of the electrical circuit. Such a 
connection is called a ground return circuit (Fig. 7). 

Where a current travels entirely by wire it is called a 
metallic circuit. 

The ground return circuit is used extensively in telegraph 
work, and sometimes for telephones. Lighting circuits are 
always metallic. Trolley circuits use the rails for the 
return. 



Chapter XII 

MAGNETISM 

THE natural magnet, or lodestone, is but a piece of iron 
ore. These magnetized stones were picked up in 
ancient Lydia and carried to the city of Magnesia, from 
whence they take their name. Lodestones are a very rare 
form of iron ore. They are still found in Asia, in Norway 
and Sweden. Just how they become magnetized no one 
knows. The lodestone was a toy which puzzled students 
and philosophers for ages, because it attracted and held bits 
of iron and steel. It was of no use to civilization until it 
was accidentally discovered that a lodestone would always 
swing around and point toward the poles of the earth when 
it was suspended from a cord or balanced on a pivot. By 
another accident it was discovered that steel needles could 
be magnetized by rubbing them on the lodestone. 

These magnetized needles showed a strong tendency to 
point toward north and south when free to turn in answer 
to the mysterious force. Out of this was born the mariner's 
compass. 

It was Gilbert who discovered that the earth is a huge 
magnet. He also showed that the earth poles and the 
poles of a magnetic needle are opposed to each other. It 
is always the south pole of the compass which points toward 
the north pole of the earth. But for convenience' sake we 
always speak of it as the north pole. 

io6 



MAGNETISM 

The magnetic north of the earth is not the true north. 
In fact, the north pole and the magnetic north are a long 
ways apart. The magnetic north is near the arctic circle 
in northern Canada. The south magnetic pole is near the 
antarctic circle, and not at the south pole of the earth. 

The north magnetic pole, or area, lies in the vicinity of 
King WiUiam's Land, just ofF the arctic coast of North 
America. These are strange lands that we don't hear 
much about. 

When this magnetic pole is between us and the north 
pole the compass points due north. As we go either east 
or west from this line it is easy to see that the compass is 
"off" to a certain extent. If we were to travel north of the 
magnetic pole the needle would point south; west of it the 
needle would point east. 

The Earth's Magnetic Poles 

Sir James Ross, in 183 1, located the north magnetic pole, 
approximately, at a point up in Bothia. In 1903 Captain 
Ronald Amundsen (who recently discovered the south pole) 
in the good ship Gjoa, set out on an expedition which lasted 
till 1906, and during those three years he relocated the 
magnetic pole and incidentally made the "Northwest 
Passage," the goal for which mariners have striven since 
the days of Hendrik Hudson. 

Amundsen and his assistants lived for nearly two years 
in King WilHam's Land, west of the coast of Greenland. 
This was about one hundred nautical miles from the mag- 
netic pole, and is a favorable point for making magnetic 
observations. 

Terrestrial magnetic force is different on every part of 
the earth's surface, and is not always the same at a given 

107 



HARPER'S BEGINNING ELECTRICITY 

point. It is subject to regular daily and yearly changes, 
and Amundsen wanted to find out about these changes. 
Evidently, the best place would be near the seat of the mag- 
netic power, so there he posted himself, and for nineteen 
months, day and night, his party took readings of their 
instruments. 

Amundsen himself also made short excursions right into 
the very region of the magnetic pole, and was able, by the 
aid of observations, to prove absolutely that the magnetic 
north pole does not have a stationary situation, but is con- 
tinually moving. 

These movements are called variations or deflections of 
the magnetic north. 

If the earth has a magnetic north and a magnetic south, 
it must have a magnetic equator. Only at the magnetic 
equator can the compass needle be truly balanced. The 
farther north you go the more the point of the compass 
needle will be attracted downward toward the earth. 
This is called the dip or inclination of the needle. South 
of the imaginary magnetic equator it is the so-called south 
pole of the magnetic needle which dips toward the surface 
of the earth. 

The government at Washington has prepared elaborate 
magnetic maps of the earth's surface. These maps are of 
great service to surveyors who must figure on the variations 
of the magnetic needle from year to year in order to run 
their Hues correctly. Without allowing for these varia- 
tions, surveys made a hundred years ago might not be near 
where the needle would indicate to-day. 

It is easy enough to prove that the earth is a magnet. 
With a pocket compass and a bar-magnet it can be demon- 
strated to the most skeptical. The bar-magnet has a north 
pole and a south pole, and the center of the bar can be said 

io8 



MAGNETISM 

to be the magnetic equator. Lay the magnet on a level 
surface pointing north and south. Hold the compass over 
the center of the magnet and the needle will be nicel}^ 
balanced. Advance it slowly toward the north pole of the 
magnet and the point of the needle will begin to dip. The 
nearer the compass approaches the north pole of the mag- 
net the more the needle will tip downward. When the com- 
pass is brought toward the south pole the other end of the 
needle will dip. 

Electric storms disturb the magnetism of the earth. The 
sun and moon have some influence on the earth's magnetism. 
The great northern aurora proves the presence of electrical 
disturbances in the air. 

Because of these electrical disturbances the compass 
needle is never at rest. It trembles and oscillates, showing 
that the lines of force of this great magnet called the earth 
are constantly disturbed. 

Magnetism and Its Effects 

A number of metals readily acquire magnetism, but most 
of them only in a slight degree. Iron and steel make the best 
magnets. Nickel, cobalt, and several of the so-called rare 
metals can be magnetized a little. 

Soft iron acquires magnetism, but loses it instantly. 
Steel absorbs magnetism and retains it for long periods. 
All permanent artificial magnets are of steel. The nature 
of the lodestone is much the same as steel. 

There are two kinds of permanent magnets. The har~ 
magnet is a straight bar of steel. The horseshoe-magnet is a 
U-shaped piece of steel. 

A good bar-magnet will suspend from five to seven times 
its own weight. A good horseshoe-magnet will hold twenty 

109 



HARPER'S BEGINNING ELECTRICITY 

times Its weight of metal. A wrought-iron electro > : . : hav- 
ing a core one inch square can be made to carry ijfoo pounds. 

The magnetism in a steel bar seems to be mosth* on or 
near the surface. By etching off a thin him of metal with 
a strong acid most of the magnetism vanishes. 

The earth will magnetize a bar of steel if it is laid for a 
long time parallel to the earth's magnetic lines, which are 
north and south. Steel can be magnetized b}* rubbing it 
on a magnet. The fact that the magnetism is more quickl}^ 
acquired if the steel bar to be magnetized is hammered dur- 
ing the process seems to prove that magnetism affects the 
molecules of the steel. 

With a steel magnet innumerable other magnets can be 
made b}^ contact with it and zi'ithont its losing any ma^K:::s?n. 

A steel bar will hold onl_v a certain amount of magnetism. 
\^Tien this amount is attained it is said to be sarwaud. Any 
magnetism above this capacity will vanish as soon as the 
current is removed. 

Even a U-shaped steel magnet will lose its magnetism 
after many years. To prevent this loss it is provided with 
an armature, or keeper, which is placed across the poles to 
complete the magnetic circuit and prevent this loss. 

Magnets lose their power when heated red-hot or cooled 
to vet}' low temperatures. A violent concussion will also 
remove the magnetism. 

Soft iron quickh' loses most of the magnetism imparted 
to it. Onh" a very small proportion is left. This is called 
res idual rr. a i ?: e: {; rn . 

Similar poles of magnetic needles always repel each other. 
Opposite poles alwa3^s attract each other. This is wh}- the 
south pole of a compass always points toward the north 
pole of the earth. 

We cannot produce a north pole in a magnet without its 

no 



MAGNETISM 

companion, the south pole. Place two bar-magnets of the 
same size and strength end to end and they will have but 
one north and one south pole. 

Break a magnet up into pieces, and each piece will show a 
north and a south pole. Put the pieces together again, 
and there will be but one north and one south pole. 

We do not know what magnetism is. We do know many 
of its actions and the natural laws which govern this force. 

Different Kinds of Magnets 

There are two kinds of magnets, artificial and natural. 
There are also two kinds of artificial magnets, the permanent 
magnet and the electromagnet. Natural magnets are always 
lodestone or bits of iron ore. Permanent magnets are al- 
ways made of steel. Electromagnets are of soft iron wound 
with insulated wire. The magnetism of the latter is due 
to the inductive influence of an electric current passing 
through the wire. This magnetism vanishes when the cur- 
rent ceases to flow. 

There is a diff'erence between magnetism and electric 
current. Magnetism seems to be the product, or result, of 
electricity. It is presumed that the molecules of the steel 
are polarized, which produces the magnetism. 

Steel magnets should never be more than a quarter of an 
inch thick to be eff'ective. If greater strength is required 
it can only be secured by duplicating the magnet and plac- 
ing the dupHcates side by side. A single steel bar of the 
same size and weight as a number of thin steel magnets 
fastened together with a strip of brass will not give as much 
magnetism as the combined magnets. The steel should 
always be of the best and finely tempered. The harder the- 
steel the longer the magnetism will be retained. 

Ill 



HARPER'S BEGINNING ELECTRICITY 

A magnet cannot impart to a steel bar a greater quantity 
of magnetism than its own. But a number of steel mag- 
nets can be charged from one magnet without decreasing 
the magnetism in the least. If these magnets are all bound 
together their combined magnetism will be far greater 
than the original. By reversing the process the magnetism 
of the original can be raised to the saturation point. 

The permanent magnet has never advanced beyond the 
toy stage, except in compasses and magnetos. The compass 
is a small permanent magnet made in the shape of a needle, 
or an arrow, and balanced on a pivot so that it can swing 
around and obey its impulse to point north and south or to 
parallel the lines of magnetic influence between the north and 
south poles of this magnetic earth. 

The Electromagnet 

The electromagnet is indispensable to almost every mod- 
ern application of electricity. Without electromagnets the 
dynamos and motors could not run; the telegraph would 
refuse to carry its messages around the world; the telephone 
would not transmit your voice the length of the room; 
wireless would not work; fire alarms would be worthless; 
and door-bells would refuse to ring. The electromagnet is 
what might be termed an "artificial magnet." That is, we 
may put the magnetizing force into it or take it away at will. 

We know that a wire carr34ng current has formed around 
it a field of magnetic force, which is as strong, in proportion, 
as the strength of the current flowing in the wire. The 
theory is that this field of force is of the nature of invisible 
lines of force encirchng the wire, and as you look along the 
wire in the direction in which the current flows the lines are 
circling around the wire in the direction of the hands of a clock. 

112 



MAGNETISM 

This, you must understand, is theory so far. No one can 
see the lines of force, but the theory fits the facts of phe- 
nomena which we are able to observe. And as long as the 
theory does not "fall down" before the results of actual 
experiment we may safely base our arguments upon it. 

If you take that same wire which is carrying current and 
form it into a spiral coil you have what is called a solenoid. 
Remember that the lines of force are still encircling the wire 
in each individual turn of the spiral. Therefore, the ten- 
dency is for all these lines of force to thread down through the 
hollow spiral and up along the outside, or vice versa, depend- 
ing on which end of the solenoid you are looking at. Then, 
strange to say, the solenoid, as a whole, takes on the proper- 
ties of a bar-magnet. That is, one end of the solenoid is a 
north pole and the other a south pole. Suspend it carefully 
by its middle, and it will point to the north magnetic pole 
of the earth, the same as a compass needle. All this, re- 
member, is due to the current flowing in the wire. 

Slip inside the coil a bar of iron, and we have an electro- 
magnet. Turn on the current, and the iron bar becomes a 
powerful magnet — many times stronger than any per- 
manent magnet ever made. Its strength depends upon the 
strength of the current flowing in the wire and the number 
of turns of wire in the coil, called the ampere-turns. Turn 
off" the current, and the iron ceases to be a magnet, except 
i for a very little residual magnetism. The explanation is 
I that the lines of force threading through the coil saturate 
the iron with magnetism to a far greater extent than any 
I other known way of magnetizing. 

\ An electromagnet is simply a bar of soft iron around which 
i is wound a coil of insulated wire through which flows a cur- 
I rent of electricity. 



Chapter XIII 

THE LINES OF MAGNETIC FORCE 

INVISIBLE lines of magnetic force surround every mag- 
net, every body charged with static electricity, every 
conductor carrying a flow of electricity. 

These lines extend for a considerable distance from the 
magnetized body. This distance is known as the field of 
force. 

We know that this field of force exists because a compass 
needle will show an electrical disturbance if brought within 
the reach of the invisible rays. These same magnetic lines 
of force inclose an electrified wire like a tube. They flow 
from pole to pole in all magnets, radiating out in every di- 
rection, forming an invisible spheroid about the magnet. 

It is thought that these rays consist of magnetized air, or 
ether, molecules. Certain it is that air is a non-conductor of 
electricity, and the atmosphere surrounding a magnet must 
be aff'ected by the magnetic influence. To send these invisible 
rays of force out into the air requires energy. This energy 
is imparted to the magnet at the time it is magnetized, and 
must, necessarily, waste away in the course of time. 

Demonstrating Magnetic Rays 

Magnetic rays cannot be seen, but they can be very 
easily demonstrated. Lay a sheet of writing-paper on top 

114 



THE LINES OF MAGNETIC FORCE 

of a bar-magnet or across the poles of a horseshoe-magnet. 
The paper should be supported until it lays very smooth 
and level. Now dust the paper with very fine iron filings, 
tapping the paper with a lead-pencil to assist the fi.lings in 
adjusting themselves to the lines of force. 

As each grain of iron falls upon the paper it is made a 
tiny magnet by induction. Each will have a north and 
south pole. Each north pole will be attracted by the south 
pole of the magnet, and each south pole will be attracted 
by the north magnetic pole. These tiny magnets will ad- 
just themselves parallel to the lines of force flowing from 
the magnetic poles, just the same as the compass needle 
adjusts itself to the earth's magnetic lines of force. In this 
way the iron filings will mark out the curved lines of force 
so that they may be seen (Fig. i). 

It will be seen that the lines of force emanating from the 
north pole of the magnet are attracted by the south pole. 



nm 




Fig.f 




Fig. 2 



The lines of force emanating from the south pole are at- 
tracted by the north pole. This forms a spheroid of in- 
visible lines of force around all parts of the magnet. 

The paper and filings show only a flat plane. It must 
8 115 



HARPER'S BEGINNING ELECTRICITY 

be remembered that these lines of force are the same all 
around the magnet. 

The spherical construction of these lines of force is best 
shown with a powerful magnet of the horseshoe type. A 
thin glass plate is laid across the poles of the magnet. Iron 
filings are dusted slowly and carefully upon the glass over 
the magnetic poles. In this case the magnet will be power- 
ful enough to overcome the force of gravity, and the iron 
filings will pile up in spherical form (Fig. 2). 

The iron filings can also be used to illustrate the repulsion 
of two similar magnetic poles. 

Lay two bar-magnets on the table a couple of inches 
apart, so that the north poles oppose each other. We 
know from previous tests that these two poles must repel 
each other. Cover with a sheet of writing-paper and dust 
with iron filings. The filings will adjust themselves into 
curves which will illustrate how such lines of force repel 
each other (Fig. 3). 

Penetrating Powers of Magnetic Rays 

It will be noticed in these tests that paper, glass, cloth, 
wood, cardboard, and similar substances offer no apparent 
resistance to the lines of magnetic force. The rays seem to 
pass readily through them as easily as hght-rays pass 
through clear glass. Steel and iron absorb the rays. Other 
substances, such as bismuth and copper, turn aside or repel 
the rays. Substances which cannot be magnetized are 
called diamagnetic bodies. 

With the aid of a magnet any one can test out materials 
and arrange them in classes headed magnetic and dia- 
magnetic. 

Another way to examine the ray effect of magnetic lines 

116 



THE LINES OF MAGNETIC FORCE 

of force is to fill a glass tube with loose iron filings. A thin 
cork is placed in each end of the tube to keep the filings from 
spilling. When a magnet is placed against one end of the 
tube the rays will easily penetrate the cork and communicate 
with the filings. Instantly the filings will become mag- 
netized by induction, and will arrange themselves along the 
lines of force. 

Another evidence of these magnetic rays is the fact that 
a magnet will last longer if provided with an armature^ or 
keeper, of soft iron. If the magnetic rays have to force 
their way through the air resistance they soon become 
weaker. If a keeper is placed across the poles of the magnet 
these rays travel the easiest path, which is through the soft 
iron. Meeting with less resistance in the iron, they do not 
weaken so fast, and the magnet retains its power longer. 

Lines of magnetic force surround every wire carrying an 
electric current. This can also be easily proven by thrust- 
ing the wire through a sheet of paper and dusting the paper 
with iron filings. The filings will quickly arrange them- 
selves in a circle about the wire (Fig. 4). 

Of course, the extent of these circles depends upon the 
force of the current passing through the wire. It makes 
no difference whether the wire is insulated or not, these 
lines of force will still exist to the same extent. 

The air-space about a magnet is quite filled with these 
invisible rays. They seem to start from the north pole of 
the magnet and curve around through the air to the south 
pole and return to the north pole through the body of the 
magnet. 

Explaining the North and South Poles 

Wherever these rays enter a magnetic substance a south 
pole is created and a north pole appears at the point where 

117 



HARPER'S BEGINNING ELECTRICITY 

the rays leave the substance. When a piece of iron is 
brought near the north pole of a magnet the rays instantly 
rush into it, creating a south pole, and out of the other end, 
creating a north pole. As these lines of force are always 
under tension and tend to shorten themselves, the piece 
of iron is attracted toward the magnet. The stronger the 




Fig. 5 

magnet the more hues of force it has and the greater its 
attraction. 

If the currents in parallel conductors flow the same way 
the lines of force which encircle each wire tend to merge 
into a single line. The tension of these lines will attempt to 
pull the wires together. If the currents flow in opposite 
directions the lines cannot merge, and the wires will repulse 
each other. This fact can also be illustrated with a sheet of 
cardboard and a few iron filings (Fig. 5). 



Theory of Magnetism 



It is difficult to explain the magnetism in a piece of steel. 
It is all a matter of theory. In the electromagnet modern 

118 



THE LINES OF MAGNETIC FORCE 

theory holds that the soft-iron core is magnetized by the 
hnes of force in the coils. According to this theory, each 
molecule of iron is instantly made into a tiny magnet, and 
all are free to turn easily and quickly to a position parallel 
with the Hnes of force. This changes them into a single 
magnet with only one north and one south pole, and the 
energy of each tiny magnet is thus added to the whole. 
As there are millions and millions of these tiny molecules, 
even in a small electromagnet, the sum-total of the mag- 
netic influence is enormous. When the electric current is 
turned off and no longer produces lines of force about the 
coils the soft-iron core loses its magnetism. Rather, each 
little molecule loses its magnetism, and they resume their 
former haphazard position in the core. 

Steel is soft iron hardened by a tempering process. There- 
fore, its molecules are very close together and can turn 
about only with extreme difficulty. Once in position they 
remain so for a very long time. When the steel is mag- 
netized the molecules slowly take position parallel with the 
lines of force emanating from the source of magnetism. 
Once this position is assumed they cannot readily change 
back, and so they remain magnetized for a long time. 

This theory seems very logical, and it may be true enough, 
although it has never been very firmly established. 

In order fully to understand electromagnetic machinery 
it is necessary to comprehend the lines of force about a 
magnet. We know that sound-waves travel through the 
air, although we cannot see them. We know that wireless 
electric waves pass through the air, and they cannot be 
seen by mortal eyes. We must realize that lines of force 
exist between and about the poles of a magnet, even though 
they cannot be seen. 



Chapter XIV 



A. ^ _- _ _ _j"- several metals can be magnetized, iron 
and s:eel alone are used for magnets. 
The firs: ":":?. or lodestones, were undoubtedly pro- 
duced b ir: :„^n from earth currents, or by static dis- 
c: : t5 £:7 7- bars and tools have been known to be 
::zr i : : : ; it of lightning striking near by. It has 
: - snovTQ that ir.a ^re:s can be produced with 
t.zziz.dty. 

I: 1 bar of steel be laii riri. :: zne earth's magnetic 
currents, north and south, it will in time beciT.e rriiz- 
rr::i7^ to a certain extent. 

- :ed before, soft :::" is eis . magnetized, but loses 
its :::\^rr:-5~ : :t s c: I: :: is iron is first hardened, 

_: : ::5 \: sttt. i:t r-ziri : r. : rr.i^r.zz znty will become 
:v.izr.zzzzzi. o :.:':z:zz '^zzz. r-"s. r.tzi'.eSy knife-blades, 
etc., on a pocket r:; .:r -. : ey will become magnetized. 

The Ba„--Magr.et 

A straight magnet, called a ^ar-magnet, can be very easily 
made. Secure a piece of tool-steel about six inches long, 
one inch wide, and one-quarter inch thick. This iron should 
be sawed off so the ends will be smooth, and not cut with a 

I20 



PERMANENT AND ELECTROMAGNETS 

cold-chisel, which leaves a rough end. Heat the iron on the 
gas-stove or in the coal-stove until it is bright red all over, 
then plunge it in a bucket of cold water. This will make 
it very hard. By varying the degree of heat from a dull 
red to a bright cherry the bar can be given any temper 
desired. The harder it is made the longer it will retain its 
magnetism. 

After the soft-iron bar is made into steel by this temper- 
ing process it should be cleaned very thoroughly. There 
are a number of ways of magnetizing the steel bar. The 
easiest way is to rub it with another magnet. Lay the bar 
on the table; place the north pole of a pocket magnet on 
the center of the bar, and draw it slowly toward one end. 
Remove it, and repeat this twelve times. Now place the 
south pole of the magnet on the center of the bar and rub 
the other way twelve times, and the bar will become mag- 
netized. 

The bar can also be magnetized by placing it inside a coil 
of insulated wire through which is sent twelve heavy static 
discharges. Care should be taken to send this static cur- 
rent always in the same direction, or it will have a neutraliz- 
ing effect on the bar. The bar can also be magnetized by 
bringing it very near the poles of a powerful generator. 

Bar-magnets made in this way are apt to lose their mag- 
netism, owing to the extreme length of the lines of force 
which waste their energy forcing their way through the air. 
To keep bar -magnets in good condition two should be 
placed side by side, separated by a piece of wood, with their 
opposite poles together, and connected by a piece of soft 
iron (Fig. i). 

The *' keeper" at the ends will be held securely in place 
by attraction and will provide an easy path for the hnes of 
force, thus helping to preserve the strength of the magnet. 

121 



HARPER'S BEGINNING ELECTRICITY 
The Horseshoe- Magnet 

Magnets made U-shaped are called horeeshoe-inagnets. 
The}^ are best because they retain their magnetic strength 
longer than bar-magnets, owing to the shorter path of the 
lines of force from pole to pole. A piece of tool-steel twelve 
inches long, an inch wide, and a quarter of an inch thick 
can be easily forged into a horseshoe shape by heating it in 
the fire and hammering it on the anvil. A gcxxl blacksmith 
can shape one and temper it in a very few minutes, and at 
small cost. 

To magnetize a horseshoe-magnet lay it flat on the table, 
with its ends touching the poles of another horseshoe-mag- 
net. Lay a short piece of soft iron, or keeper, on the bend 
of the magnet and rub slowh^ toward the opposite end of 
the steel to be magnetized. Do this twenty times, taking 
care to lift the keeper after every stroke. Then turn the 
magnet and the steel over without altering their position 
and repeat the operation on the other side (Fig. z). 

This will produce a very powerful magnet. If the poles 
are changed during the operation it will have a neutrahzing 
effect, and no magnet will result. It is best to mark the 
poles on the steel before starting, and then place the north 
pole of the magnet against the south pole of the steel to be 
magnetized. 

A bar-magnet can also be magnetized by stroking it with 
two bar-magnets, beginning at the middle and rubbing tow- 
ard the ends. In this case the north pole of one magnet 
should rub toward the south pole of the bar, and the south 
pole rub toward the north pole (Fig. 3). 

Magnets can also be produced hy induction. Wind the 
bar of steel with insulated copper wire. Use a large wire 
for a strong current, taking only a few turns about the bar. 

122 



! PERMANENT AND ELECTROMAGNETS 

For a weak current use a fine wire and many turns. When 
i a current is forced through this wire by the batteries, it will 
magnetize the steel by induction. 



I A Magnetizing-Coil 

i 

I While experimenting with magnetism it is best to make 

I a coil purposely for magnetizing objects by induction. 

i Roll up a sheet of heavy cardboard to form a hollow tube 




Fig. 3 



Fig. 5 



a Httle over an inch in diameter and three inches long. 
Fasten with glue. Provide this core with two wooden end- 
pieces cut from a cigar-box to form a flat spool (Fig. 4). 
Lay four pieces of insulating tape along the spool, and over 
I the edge. Wind the spool with heavy cotton-insulated wire. 
! When filled bring up the ends of the tape and fasten firmly 
I in place. Remove the end-pieces and draw out the core. 
j The core is now held in shape by the tape, but it should be 
j given a couple of coats of shellac varnish to thoroughly in- 
I sulate it. When dry connect the ends of the coil to three 

123 



HARPER'S BEGINNING ELECTRICITY 

dn'-cell batteries, in series, and the coil can be used to 
make magnets (Fig. 5). 

This coil can be mounted on a wooden base for convenience 
in operation. If a piece of steel is placed in the coil, and 
the current turned on, it will be magnetized by induction. 
Frequent interruption of the current, by turning it on and 
off, helps in the making. Tapping the ends of the bar with 
a light hammer will also hasten the operation. 

One of the first experiments with this magnetic coil 
should be to magnetize a long steel knitting-needle. Test 
its magnetism with the compass, and mark the north and 
south pole. Dipping the north end in a tiny bit of hot 
sealing-wax is a good way to mark it for identification. 
Now break up the knitting-needle into small pieces. The 
compass will show that each piece has changed into an in- 
dividual magnet. Arrange these pieces back into position 
and the needle will again be a single magnet. 

As soon as a number of bar-magnets have been made two 
should be suspended b}^ silk threads, so that they are free 
to swing easily. In this way you can prove that like poles 
of two magnets always repel each other, and that opposite 
poles always attract each other. 

Playing with Magnets 

Another interesting experiment is to magnetize a number 1^ 
of steel needles of equal size. Half the needles should be j 
magnetized so that the heads are the north poles, and half , 
with the points as north poles. Thrust the needles through .i 
circular pieces of cork and place in a basin of water. In- 
stantly the heads will float away from each other. The 
points will also repel each other, but the heads and points 
will attract each other. The needles will assume various 

124 



PERMANENT AND ELECTROMAGNETS 

geometrical figures in performing these evolutions. They 
can be made to change places and float about by approach- 
ing them with the end of a bar-magnet. 

From this it will be seen that a number of very interesting 
toys can be made by whittling soft wood, or cork, into 
various shapes and embedding a tiny magnet in each. A 
whole flock of ducks can be made in this way which will 
readily follow a woman with a basket of food under her arm, 
but will be terribly shy of a man with a gun on his shoulder. 
The trick is done by giving all the concealed magnets in 
the ducks the same ending — pointing all the north poles 
outward. In. the basket of feed is concealed a small mag- 
net with the south end arranged to point toward the ducks. 
Thus the ducks are attracted by the woman. The gun is 
a tiny bar-magnet with the north pole outward, which re- 
pels the ducks, causing them to fly away. 

It is fooKsh to try to suspend a bar of iron in the air by 
balancing it between the pull of gravity and the attraction 
of a magnet. By fastening the ends of the iron bar down 
with fine silk thread and suspending a powerful magnet 
above it, the bar can be lifted and made to appear as though 
it was suspended. In reality the magnetic force is greater 
than the pull of gravity, but the thread prevents the bar 
from flying to the magnet. 

A small steel bar-magnet can be balanced in the air by 
placing it in a spiral coil, or helix, made of insulated copper 
wire. When the current is turned on the steel magnet will 
be seen to jump up and remain suspended in the middle of 
the helix. This is caused by the lines of force surrounding 
the wire coils of the helix and the repulsion of the fines of 
force from the magnet. 

Soft iron is magnetized by induction when it is brought 
near a permanent magnet. Hold a bar of soft iron very 

125 



HARPER'S BEGINNING ELECTRICITY 

near a permanent magnet, and the bar will evidence all the 
properties of a permanent magnet. Of course, this magnetism 
ceases the instant the iron is taken away from the inductive 
influence of the permanent magnet. It is magnetic only so 
long as acted upon by the lines of magnetic force surround- 
ing the permanent magnet. 

Making an Electromagnet 

Upon this principle all electromagnets are made. A cop- 
per wire carrying an electric current is surrounded with 
many spiral rings of magnetic force. This is proven by the 
writing-paper and iron-filings test. If soft iron can be made 
magnetic by bringing it within the lines of magnetic force, 
and every copper wire is surrounded by such lines of force, ' 
then to magnetize soft iron it is only necessary to wind it i 
with an insulated wire, through which is flowing an electric | 

current. ' 

i 

If several turns of insulated copper wire are taken about i 
a bar of soft iron the iron can be made magnetic at will by | 
turning on and off the current. By winding the end of the f 
iron bar with a spool of insulated copper wire a very power- I- 
ful magnet is produced whenever a current is flowing F 
through the wire. The current itself may be very weak, 
but the magnetism of the wire is multiplied by every turn 
until it totals an enormous force (Fig. 6). 

By bending a round bar of soft iron into U-shape, and 
slipping a spool of insulated wire on each extremity, con- 
necting the spools together and placing them in circuit 
with a battery, a powerful magnet is produced (Fig. 7). 

It makes no difference in which direction the iron bar 
is wound, whether from right to left, or reverse, providing 
the winding is always in the same direction. If, at any time, 

126 



PERMANENT AND ELECTROMAGNETS 



the winding of either pole is reversed, it causes opposing 
poles and has a neutralizing effect. 

Electromagnets have greater strength, in proportion to 
their weight, than steel magnets. They can be made as 
large as desired. As their magnetic strength is always in 
proportion to the size of the iron core, the amount of in- 





Fig. 7 



Fig* 6 

sulated wire in the coils, and the amount of current used, 
it is apparent that there is no limit to the possible size of 
the electromagnet. 

The iron core of an electromagnet cannot be magnetized 
beyond its point of saturation: For this reason the core 
must always be in proportion to the coils. The diameter of 
the coils does not influence the strength of the magnet 
very much beyond certain limits. Too many coils are inad- 
visable. The diameter of the coil should not exceed one- 
half its length. The core should always be of the very best 
soft iron, projecting a Kttle beyond the coils. The coils can 
be made separately and slipped on and off the core at will. 

A good experimental electromagnet can be made from a 

127 



HARPER'S BEGINNING ELECTRICITY 

common iron bolt and fift}' feet of No. 24 insulated copper 
wire. Select a rather thick bolt about five inches long. 
Cover the space between the nut and the head with a layer 
of stiff writing-paper fastened with paste. When thorough- | 
ly dry put on a layer of wire, starting at the nut and leaving 
an end a foot long for connection with the battery. Wind 
the wire smooth and tight, with each turn laying snug 
against its neighbor. When you reach the head, turn and 
wind back to the nut in the same way. Put on six la3'ers, 
which should bring the end of the wire back to the nut, 
with about a foot left for connection with the battery. 
Paste a thick layer of paper over the top coil to protect it 
from injury, and the electromagnet is done. To operate this 
magnet it is only necessary to scrape the insulation from 
the ends of the wire and connect with the batterv (Fig. 8). 

The Solenoid, or Magnetic Coil 

The relationship between magnetism and electricity is eas- 
il}^ show^n by constructing a simple helix of copper wire with 
the ends returning through the center of the coil (Fig. 9). 

This device is called a solenoid. When it is placed in cir-* 
cuit with a battery it possesses magnetic poles. If suspended 
so as to be free to turn, it will point north and south. Its 
north and south pole can also be determined with the aid 
of a compass needle. The north pole of the needle will be 
repelled b}^ the north pole of the solenoid, and the south 
pole of the compass will be attracted by the north pole of 
the solenoid. 

Another type of solenoid has the peculiar power to pull an 
iron core into the coil whenever a current is sent through 
the coils of wire. Construct an eight-inch tube of stiff card- 
board one-half inch in diameter and wind it closely with 

J28 



PERMANENT AND ELECTROMAGNETS 

insulated copper wire, giving it as many layers as desired. 
Set the solenoid upright on the work-table. Over it sus- 
pend by a long rubber band a three-eighth-inch soft-iron rod 
eight inches long (Fig. lo). 

When a battery current is sent through the wire coils 




Fig. 9 



Fig. to 



of the solenoid the iron core will be drawn down into the 
coil. When the current is turned off the rubber band will 
draw out the core, and the operation can be repeated. 

The sucking action of the solenoid can be made continuous 
by arranging the iron core so it will trip a small switch when 
it enters the coil and so disconnect the current. Instantly 
the core will be drawn back, striking a lever which closes 
the circuit, and the solenoid draws it in again. 

How the Electric Bell Rings 



One of the common adaptations of the electromagnet i? 
the electric door-bell. It is hard for the amateur to under- 

129 



HARPER'S BEGINNING ELECTRICITY 

stand how the touching of a button on the front porch will 
ring a bell in the kitchen. 

The electric bell is a very simple device, taking a little 
current from a battery. The little button on the door- 
jamb is a spring device which keeps the circuit open between 
the battery and the bell. The pressure of a finger closes the 
circuity and the electricity flashes over the line to the bell. 
The bell itself is somewhat more intricate than it looks. In 
the Httle box beneath the bell are two small coils of fine 
insulated wire wrapped tightly about soft-iron cores. Of 
course, w^hen electricity flows through the insulated wire of 
these coils the soft-iron cores become magnets. These mag- I 
nets attract a soft-iron plate attached to the lower end of 
the bell - clapper. This iron plate is fastened to a steel 
spring, but the magnets are powerful enough to overcome 
the action of the spring and to pull the plate toward it. j,. 
This action pulls the clapper down, and at a certain point 
the plate breaks the electric circuit, destroying the pulling 
force of the magnets, and the steel springs throw the clapper 
back against the bell. Of course, the circuit is then closed 
again, and the action is repeated as long as the button is 
pushed. 

Electricity moves at astonishing speed, and this vibrat- 
ing action is repeated until the bell rings faster than anyj 
one can count, providing the finger is kept on the connecting 
button. 



Chapter XV 

THE INDUCTION-COIL 

ANY conductor is electrically excited when moved con- 
i\ tinuously within the lines of force about a magnet. 

Electric currents produced in this way are caused by 
induction. 

If a magnet is thrust into a spiral coil of wire which is 
i connected with the galvanometer, the instrument will show 
that a current has been induced in the coil. The galva- 
nometer will also show that this current stops when the 
motion ceases, or when the magnet is at rest. When the 
magnet is pulled out of the coil a current is again induced, 
hut it flows the other way. 

Prepare a small coil of insulated wire. Electrical en- 
gineers speak of this coil as the primary. 

Make another coil somewhat larger, with a bore large 
enough to admit the primary coil. This large coil is known 
as a secondary. 

Connect the primary coil with an electric battery. Con- 
nect the secondary coil with the galvanometer (Fig. i). 

If the primary is inserted in the bore of the secondary the 
galvanometer will show that a current of electricity has been 
generated in the coils of the secondary. When the primary 
coil is withdrawn another current is generated which flows, 
in the opposite direction. 

9 131 



HARPER'S BEGINNING ELECTRICITY 

An Explanation of Induction 



I 



The simple statement that such a current of electricity 
is created by induction is hardly an explanation. Perhaps 
it is more comprehensive to say that the insertion of the 
primary coil into the secondary coil cuts the lines of mag- 
netic force. This creates a difference of potential between 




I 



Fig. f 

that part which cuts the lines of force and that which does 
not. Current cannot be produced without a difference of 
potential, so the insertion of the primary must have this 
effect and must produce a current. 

There is a current when the primary is inserted, and an 
other when it is withdrawn; but when the coils are at rest 
the instrument will not record any flow of electricity. This ^ 
same effect can be duplicated by leaving the primary coil ^ 
inside the secondary and turning on and off the current from - 
the battery. It will be noted that a flow of current is pro- ; 
duced in the secondary each time the current is sent through '. 

132 



s \^ 



THE INDUCTION-COIL 

the primary, and another flow of current each time the cur- 
I rent it turned off". When the primary circuit is rapidly 
I closed and opened a "make" and "break" current is pro- 
I duced. 

When this process of electrical induction is understood 

it is easy enough to make a spark induction-coil. Such a coil 
j will produce a current of very high potential closely related 
I to static electricity. In fact, nearly every static experiment 
i can be duplicated with an induction-coil, showing the close 
I relationship between the two phases of electricity. Such a 
\ coil can be made large enough to produce brilliant sparks 

several inches long. They have been made large enough 

to produce a spark several feet in length in laboratory tests. 

Making an Induction- Coil 

An induction-coil is as interesting as a static friction- 
machine, and is quite as easily made. The power of such 
a piece of apparatus depends upon its size, but for experi- 
mental purposes it is best to begin with one capable of pro- 
ducing a spark of about an inch. 

Prepare a core of soft iron seven inches long and one-half 
inch in diameter. A soHd piece of soft iron can be used 
if it is of the finest quality, but a better core can be made of 
soft -iron wire. Cut the wire into seven -inch lengths, 
straighten and form into a solid bundle one-half inch in 
diameter. The ends should be filed off" smooth. 

This iron core is used as the basis of a spool. For the ends 
cut two U-shaped pieces of hard wood one-half inch thick 
and three and one-half inches in diameter. Each piece 
I must be centered with a half-inch hole to admit the iron 
I core. The end-pieces are made flat on one side, so the coil 
I can be set up without rolling. When the end-pieces are in 
j 133 



HARPER'S BEGINNING ELECTRICITY m 

place the iron core should protrude, or stick out, a bit at 
each end. If the wire core is used, the wires should be 
placed in one at a time until they are packed very tightly. 
Bore two little holes through the right end-piece for the 
primary wire (Fig. 2). 

Winding the Primary Coil 

Cover the core with heavy writing-paper or thin card- 
board. Draw a No. 18 cotton-covered wire through the 
hole in the end-piece and wind it firmly on the coil, taking 
care that the wire is laid evenly and side by side. When 
the core is covered with one layer, double back toward the 
starting-point. This will cover the core with two layers 
of wire, and will bring the end back to the starting-point 
so it can be brought out of the hole provided for it 
(Fig. 3)- 

This completes the primary coil. 

Insulate this coil by wrapping it with heavy manila paper 
one-eighth inch thick. This paper must be laid very close 
to the rims. It is better if it is cut so as to extend up the 
wood a ways, as the secondary must be well insulated from 
the primary coil. Give the paper several coats of shellac, 
varnish when it is in place. Be sure that the varnish is 
thoroughly dry before putting on the secondary winding. 

The Secondary Coil 

The secondary coil consists of many layers of fine, in- 
sulated copper wire. A pound of No. 36 cotton or silk 
insulated wire is about right. Bore a hole through the 
right-hand rim just above the primary coil, taking good 
care not to mar the paper insulation. The secondary 

134 



THE INDUCTION-COIL 

wire is so small and delicate that it is necessary to splice 

on a bit of heavier wire for the terminals. Sphce on a 

j piece of heavy cotton - insulated copper wire. Solder the 

I joint if possible, otherwise be sure it is well scraped and 

' tightly twisted. 

I In winding the secondary care must be taken not to break 
!j the fine wire. It is easy to break this wire inside the in- 
sulation, where it is hard to detect, and if this occurs the 




coil will not work. Wind slowly and carefully. If a break 
occurs splice the wires carefully and cover with silk floss. 
The layers must be smooth and neat. Cover each layer 
with a sheet of writing-paper and give two coats of shellac. 
See that the paper turns up against the end-pieces far 
enough to prevent the next layer from touching the one 
below it. If the two layers touch at any point they are 
liable to "short-circuit" and ruin the coil. 

When the spool is full the wire should pass out of a hole 

I3S 



HARPER'S BEGINNING ELECTRICITY 

near the top of the left-hand end -piece. This terminal 
should also consist of a splice of heavier wire. Cover the 
coil with manila paper and varnish. The coil is now ready 
to be mounted on a wooden base five by ten inches, and 
about an inch thick. Two short screws through the bot- 
tom of the base into each end-piece will hold it firmly in 
place. Drill and countersink the holes for each screw 
(Fig. 4)- 

Vibrator for Induction- Coil 

A little device must now be constructed to automatically 
"make" and "break" the current. This is called an in- 
terrupter, or vibrator. A very good one can be made from 
a small piece of clock-spring. Straighten a piece three 
inches long. Drill two holes through one end half an inch 
apart. If the spring is too hard for the drill, heat one end 
a dull red and let it cool slowly. This will remove some of 
the temper. If too much temper has been taken out it 
can be retempered after the holes are drilled. A half-inch 
disk of soft iron should be riveted to the other end of the 
spring (Fig. 5 B). 

This spring can now be mounted on a little block of wood 
so the soft-iron disk is one-sixteenth of an inch away from '[ 
the soft-iron core of the coil. A small wooden post is 
mounted immediately behind this spring, in line with the 
core. Through a small hole in this post a common brass 
screw passes to engage the spring immediately behind and 
entered with the soft-iron disk (Fig. 5 A). 

The brass screw and the steel spring must be protected 
at the point of contact by some heat-resisting metal, or 
they will be quickly melted away by the passage of the elec- 
trical current. Platinum is generally used for this. Mark 
the place of contact on the spring, detach it and take it, 

136 



THE INDUCTION-COIL 



together with the brass screw, to the jeweler. He will drill 
a small hole in the end of the screw and drive in a tiny bit 
of platinum wire. He will also fasten a thin sheet of plati- 
num on the back of the steel spring. 

A circuit-interrupter to be operated by hand-power can 
be made from a small brass ratchet-wheel and a piece of 
clock-spring. The wheel is mounted in a wooden upright, 




<i 



Fig. 5 A 

so it can be rapidly revolved with a small crank. The 
steel spring is affixed to the same base, and adjusted so it 
plays against the toothed wheel. The device is connected 
in series with the battery circuit. When the crank is whirled 
the spring jumps from ratchet- tooth to ratchet- tooth, 
making and breaking the circuit (Fig. 6). 

Binding-posts must also be provided for the terminals of 
each coil. The base of the steel spring and the brass screw 
will answer for the primary coil. Two brass screws, each 
provided with two brass washers, can be set on the top outer 
rims of the coil. The terminals of the secondary coil should 
be firmly connected to these screws. It is best to solder 
each terminal wire to a brass washer. 

137 



HARPER'S BEGINNING ELECTRICITY 

Value of the Condenser 

Coils of larger size should also be provided with a ''con- 
denser/' This is a little device to prevent a heavy spark 
at the platinum points. It does this by absorbing the cur- 
rent which causes the spark at "break"' or when the cur- 
rent is suddenly turned off by the interrupter. The co?i- 
denser is made of sheets of tin-foil and paper laid alternately 
in a stack. Fifty sheets of tin-foil two inches wide and 
eight inches long will make a suitable condenser for this 
coil. Begin with several sheets of paper a little larger than 
the tin-foil. La}' on a sheet of tin-foil so that one end sticks 
out a little on the right. Cover with a sheet of paper. Lay 
on another sheet of foil with an edge sticking out to the left, 
and so on until the pile is complete. Fasten with a string 
or a rubber band. Place in a wooden or cardboard box. 
Connect the left-hand ends of foil with an insulated wire 




Big, 8 

which passes through the top of the box. Do the same with 
the right-hand pieces ^Fig. 7 . 

The condenser is now readv to be connected in series 
with the battery circuit according to the diagram Fig. 8). 

For the primary circuit three good dry-cell batteries in 
series are necessary. 

138 



THE INDUCTION-COIL 

The terminal plugs of the secondary coil should be pro- 
vided with short pieces of heavy wire brought up and bent 
to right angles so that the points are about half an inch 
apart. The induction-coil is now complete and ready for 
experiments (Fig. 9). 

How the Induction-Coil Operates 

When the current is turned on it flows through the pri- 
mary coil and magnetizes the soft-iron core. This core at- 
tracts the iron disk on the steel spring and pulls it forward, 
breaking the circuit. The instant the circuit is broken the 
iron ceases to be magnetized and the spring flies back, clos- 
ing the circuit. This motion continues with great rapidity, 
making and breaking the circuit many times a second. 
The device operates with a loud hum, caused by the vibra- 
tions of the steel spring, from whence it takes its name and 
is called a vibrator. In the course of time the platinum point 
will wear down, and the screw must be readjusted. 

These induction-coils can be made in any size. The 
larger the coil the larger the spark it will produce. Coils 
have been made in a laboratory experiment that would 
produce a spark several feet long and which penetrated a 
piece of plate glass four inches thick. 

Static Experiments Can Be Reproduced with Induction-coil 

Nearly all the experiments mentioned in connection with 
the static machine can be duplicated with the induction- 
coil, and a great many additional ones are possible. 

The induction-coil is not a generator of electricity. It 
is a transformer. It merely transforms the low potential 
energy of the battery circuit into a higher potential. The 
volume of the current is correspondingly reduced as the 

139 



HARPER'S BEGINNING ELECTRICITY 

E. M. F. is increased. There is also a loss of energy through 
resistance in the coils, etc. 

The resulting current is intermittent. The E. M. F. of 
the three battery cells is but five volts, but the discharge 
between the terminals of the secondary is at the rate of at 
least twenty thousand volts for every inch of air-space, or 
ten thousand volts for a half-inch spark. If this discharge 




Fig. 9 

is sent through the muscles of the body it will cause a 
violent twitching and sometimes a painful contraction. 

It is alwaj's best to switch off the battery current while 
making any alterations or changes in the device. 

Leyden jars can be charged from the induction-coil by 
placing the jar on an insulating sheet of glass and connecting 
one of the terminals of the secondary to the knob of the jar. 
The other terminal should be set a little distance from the 
outside coating of the jar, so the spark will jump to it. The 
Leyden jar can also be used as a condenser for the secondary 
circuit, thereby increasing the size of the spark. Place the 
jar on an insulated glass stand and connect it in shunt with 

140 



THE INDUCTION-COIL 

the secondary terminals. That is, connect one of the ter- 
minals to the outer coating of the jar with a short piece of 
wire, and the other terminal in the same way to the knob. 

Experimenting with the Induction-Coil 

A great number of experiments are possible with a good 
induction-coil. Books, glass, wood, etc., can be perforated. 
Water and other liquids can be decomposed and broken 
up into gases. Wires can be heated, melted, and even 
fused. But the most interesting effects of all can be se- 
cured with the aid of suitable vacuum glass tubes known 
to the trade as Geissler tubes. 

The most wonderful illuminating effects can be produced 
with these induced currents in vacuo. Geissler tubes are 
made of thin glass with a fine platinum wire sealed in each 
end. These wires conduct the electricity to the inside of 
the tube. Platinum is used because it is the only metal 
which expands and shrinks the same as glass. Other metals 
would break and crack the glass. The tubes are only par- 
tially exhausted of air, as a perfect vacuum is undesir- 
able. Geissler tubes can be purchased in all sizes and in a 
great variety of shapes. Some of them contain rarefied 
gases and vapors to impart wonderful color effects to the 
Hght. By the use of hydrogen, nitrogen, and carbonic- 
acid gases beautiful blue, crimson, and green lights are 
possible. 

Vacuum tubes should always be handled with the greatest 
care, as they are extremely fragile. They should be kept 
in a box lined with cotton, and never laid around on the 
work-table. A coil giving a spark an inch long will pro- 
duce good luminous effects in tubes of six inches to a foot 
in length. Do not use small tubes on heavy sparks. If the 

141 



HARPER'S BEGINNING ELECTRICITY 

platinum lead-wires get red-hot while in operation, discon- 
nect at once before the tube is ruined. 

To use the vacuum tubes they are merely connected to 
the terminals of the secondary coil. It is not necessary to 
make a firm connection where such high voltage current is 
used. Simply touching the wires will suffice. 

If no vacuum tubes are available old incandescent lamp- 
bulbs will do. Old bulbs are better than new ones, as the 
vacuum should not be too high. Better effects can be se- 
cured by pasting strips of tin-foil on opposite sides of the 
glass globe. Connections are made to these tin-foil strips. 
Lamps with broken filaments will do as well as any. 

The Geissler tubes can also be operated by a current 
passing through the body. Take the vacuum tube in one 
hand and with it touch the positive terminal of the second- 
ary. Point the other hand at the other terminal of the 
secondary, without actually touching it, and the tube will 
blaze with light. In this way a current of as high as forty 
thousand volts can be made to pass through the body of 
the operator without inconvenience, so long as the fingers 
do not actually touch the coil or any part of the apparatus. 



Chapter XVI 

THE TELEGRAPH 

AS soon as it was discovered that electricity could be sent 
iV long distances over slender wires at an incredible 
speed, scientists and inventors began to experiment with 
methods for sending messages by wire. Lesage, Lomond, 
Ampere, Schilling, Weber, Gauss, and others suggested ways 
of communicating by wire. Samuel B. Morse, a prominent 
American portrait-painter, was the first to make a com- 
mercial success of the telegraph. But Morse nearly starved 
to death before he could get any one interested in his in- 
vention. 

The word telegraph is derived from the Greek tele, mean- 
ing far, and graphoy to write. It means, literally, to write 
at a distance. And this is just what the telegraph does. 

The telegraph is an adaptation of the electromagnet. 
Previous experiment has shown that if a core of soft iron 
be wrapped with several coils of insulated wire it becomes a 
powerful magnet whenever a weak current of electricity is 
flowing through the wire. This magnetism ceases when the 
current stops. The telegraph is but an electromagnet with 
longer lead-wires and a key to "make" and '* break" the 
circuit. 

If the armature of the electromagnet be laid near its poles, 
yet not quite touching them, and long insulated wires be 
extended from the magnet to the adjoining rooms and back 

143 



HARPER'S BEGINNING ELECTRICITY 

again to the table, where they are connected to the battery, 1 
the armature will be drawn against the magnet with a 
sharp cKck whenever the current flows over the circuit. 
This is the action of a telegraph simplified. The current 
travels instantly over the long wires, magnetizing the core, 
which attracts the armature. Even very weak currents in 
the wire will exert a strong magnetic effect on the core. 

A telegraph system is called a line, or circuit. 

Current is supplied by gravity batteries, zinc and copper 
plates in blue vitriol, because a continuous circuit is necessary. 
These batteries require practically no attention, and will 
last for a long time. 

Instruments Used in Telegraphy 

The instrument for making and breaking the circuit is 
called a key. The dot and dash signals are sent with this 
instrument. I 

The device which repeats the message at the other end of i 
the line is known as a sounder. The clicks from the key are 
reproduced by the electromagnet and armature of the sounder. { 

For very long lines a device has to be employed for in- | 
creasing the strength of the current, which always decreases I 
with distance, owing to Ohm's law of resistance. This in- |; 
strument is called a relay. The relay, as its name suggests, ^ 
is operated by the line current, and its purpose is to open |) 
and close the local circuit and repeat the message to the next i 
station. 

The first telegraph systems used a recorder in place of the 
sounder. The messages were written in dots and dashes 
on a strip of paper and read by the eyes of the operator. 
These systems are still in use in Europe. American opera- 
tors soon discovered that they could read the messages quite 

144 



THE TELEGRAPH 

as well by ear and discarded the recorder for the sounder 
many years ago. 

In advanced telegraphy over long circuits the batteries 
are replaced by small electric dynamos, or generators. 
Many improvements have been made in the sending and 
receiving apparatus, so that a number of messages can be 
sent over the same wire at the same time. But for these 
pages only the simplest telegraph circuits will be considered. 

Simple Telegraph Systems 

By using a pair of buzzers, two push-buttons, and a dry- 
cell battery or two, a very simple signal system can be ar- 
ranged for short-distance work. The push-button is merely 
a little spring device to keep the circuit open until the cur- 
rent is needed. The pressure of a finger on the button 
pushes down a spring and closes the circuit. The buzzer, 
as its name suggests, is a tiny electromagnet device similar 
to the vibrator on an electric bell or the induction-coil. 
One can be made from an old electric bell by removing the 
bell and the clapper. Little buzzers are also made pur- 
posely for call-bells and signals. 

The push-buttons and buzzers are connected up to the 
line so that if a button is pushed at one end, thereby com- 
pleting the circuit, the buzzer will operate at the other end of 
the line (Fig. i). 

Signals are exchanged in the Morse code. A short buzz 
represents a dot, and a long buzz a dash. These buzzer 
systems are only good for short-line service, as the current 

i soon loses its strength in overcoming the resistance in the 
line and in the magnetic field. After a little distance the 

I current will become too weak to operate the buzzer. 

I A real telegraph line can be constructed with a little more 

1 145 



HARPER'S BEGINNING ELECTRICITY 

ettort. It IS cheaper and better to buy a key and sounder 
than it is to make them. A good sounder can be purchased 
for less than a dollar, and keys can be had for as low as 
fifty-five cents. However, this apparatus is so simple in 

LINE 



PUSH SUTTON 




BUZZER 



BATTERY 



PUSH BUTTON 




bfti^ 



BATTERY 



BUZZER 




Fig, 2 

design and construction that it can be easily made in the 
workshop. 

Making the Key 

The ven^ simplest key can be miade from two strips of 
brass, a few brass washers, and three small brass screws. 
The brass strips should be three inches long, one-half inch 

146 j 



j THE TELEGRAPH 

I wide, and about one-eighth inch thick. Drill, or punch, 
! three small holes through the first brass strip — two holes 
i near one end, and one hole near the other. The second 
I piece needs but one hole near one end. These strips are 
I mounted on a hardwood base four by three inches, and one- 
half inch thick (Fig. 2). 

Screw the little wooden knob A in place. Insert the brass 
screw B from the under side of the board, drilling a hole and 
countersinking it for the screw-head. The brass strip C is 
I fastened firmly to the board by two screws. The inner 
j screw also passes through the hole in the brass strip D, 
i leaving it free to swing in a semicircle, and connect with 
the brass screw B. The terminal wires are fastened to the 
brass screws B and E, and the key is complete. The natural 
springiness of the upper brass strip will keep the circuit 
open until it is pressed down with the knob to make con- 
nection with the screw-point in the base. When the key 
is not in use the second brass strip can be swung over to 
j complete the circuit. This must be moved away before 
I the key can be operated. 

A much better key can be made by using a small brass 
j bar mounted on a small shaft near the middle. This bar 
must have an insulated finger-piece, or knob, at one end and 
a spiral spring at the other. The line is connected to the 
brass frame and to a screw-point, as in the former key. A 
narrow strip of brass is also arranged to complete the cir- 
cuit when the key is not in use (Fig. 3). 

The usual form of telegraph key is rather more compli- 
cated, but it works on exactly the same principle (Fig. 4). 

Sounders 

A very simple sounder for short-line work can be easily 
made from two pieces of tin and a horseshoe-electromagnet. 
10 147 



HARPER'S BEGINNING ELECTRICITY 




Fig, 4 

Cut a piece of tin in the shape of the letter T according to 
Fig. 5. This tin armature is mounted before the poles of the 
magnet to produce the clicks. 

The dimensions of the second piece of tin will depend 
upon the position and size of the electromagnet. It should 



^ 



<— - li" — > 



Fig, 5 



Fig, 6 



be bent as shown in Fig. 6. Its office is to control the 
tin armature. 

The sounder is adjusted as in Fig. 7. 

Another and a better sounder can be easily adapted from 
a small electromagnet. The electromagnet is laid flat on 
a small piece of wood two inches high, and a little larger |, 
than the magnet^ and hollowed out for the coils so the iron ,< 
core is level. The ends of the core should protrude slightly 



THE TELEGRAPH 



beyond the wood. This is firmly screwed to a wooden 
;' base about four by six inches (Fig. 8). 

I A small, soft-iron armature is soldered or riveted to a 
i flat piece of soft iron in the form of a cross. The length of 
; the armature depends upon the distance between the poles 
j of the electromagnet which it must cover. The strip of 
i soft iron to which it is fastened should be twice the distance 
j between the magnet core and the bottom of the base 

j (Fig. 9)- 

The armature should be a quarter of an inch thick and 



as wide as the magnet core. The bar is the same width as 




Fig, 7 



^ ii i iiiii iiiii)i iiii i niii 



M 



A. 



■^"hole 



Fig, 8 



Fig, 9 



j the armature, and one-half as thick. A small hole is now 
i drilled through the lower end of this bar, from left to 
I right, using a one-eighth-inch drill and working very slowly 
i^nd carefully. A similar hole is drilled straight through 



149 



HARPER'S BEGINNING ELECTRICITY 

the bar half-way between the armature and the lower j 
end. [ 

The sounder-frame can be made of soft iron or brass. | 
Brass is the easier to work. It is made in the form of a flat 
figure seven. Iron or brass three-eighths inches square is f 




EARTH 



EARTH 



large enough. Two small holes are drilled through the top 
and another nearer the bottom, as indicated, and the frame 
is set firmly in the wooden base about an inch from the. 
electromagnet. The holes are threaded for large-headed 
brass screws (Fig. lo). 

The armature is mounted between the bar and the 
electromagnet, so that it is free to vibrate between the two 

150 



THE TELEGRAPH 

top screws. These screws should be adjusted so that the 
armature does not quite touch the magnet core. The arma- 
ture bar is pivoted at the lower end, and adjusted so that its 
movement back and forth is free and smooth. A rubber 
band or tiny coil-spring is fixed to this bar and the frame 
to hold the armature firmly against the screw in the back 
of the frame. The lead - wires of the electromagnet are 
brought around and afl&xed to binding-posts so it can be 
placed in the circuit. 

This sounder will need a little adjustment to work prop- 
erly, but when the screws are arranged it will prove a faith- 
ful instrument. 

When the key is pressed down the armature should be 
drawn toward the magnet core, not quite touching it. This 
will cause the bar to strike against the screw-point with a 
sharp click. When the current is broken the rubber band 
or spring will pull the armature away from the magnet 
core, which is no longer magnetized, and the bar will strike 
against the other screw-point in the frame with another 
sharp cKck. In this way it will reproduce every click of 
the key. 

Telegraph Circuits 

When the instruments are made it will be necessary to 
connect them right, or the telegraph will not work. Pre- 
suming that two sets of instruments have been made, and 
it is desirous to set up a line between two near-by houses, 
the batteries and instruments should be connected as 
in Fig. II. 

A wire return is best for short circuits. Dry-cell bat- 
teries will not last. They are not suitable for continuous 
service. It will be noted that, with this connection, the 
batteries are producing a steady and uninterrupted flow of 

151 



HARPER'S BEGINNING ELECTRICITY 

current except when the key is opened, breaking the cir- 
cuit, for sending a message. As soon as the message is sent 
the key is shut and the circuit closed. In this way the line 
is always ready to take a message. Gravity ^cells should 
always be used for telegraph work. Where a return wire is 
not used the current can be sent over a ground return. In 
this case the terminals designed for a return circuit are 
merely fastened to the water pipe, or to a piece of iron which 
is buried deep in the damp earth. 

It must be remembered that the flow of current in tele- 
graph circuits is always very weak. For this reason any 
little defect in the line will cause a stoppage of the current, 
and the instruments will not work. All joints must be very 
tight, with the metal scraped bright and clean. It is best 
to solder them. The wires must be insulated at every con- 
tact-point. 

Where the wires pass out of the house through the window- , 
frame they must be protected with hard rubber or porce- ii 
lain tubes. Insulated wires must be used for all inside 
work. Bare iron wire can be used outdoors, but it must 
be suspended from glass or porcelain insulators. Never 
allow it to touch so much as a twig. A short circuit is fatal 
to such a line. The number of cells required on a tele- 
graph line depends upon the distance, as the resistance: 
of a long wire will soon overcome a single cell. A 
good rule to follow is to use one cell for each quarter- 
mile up to a mile and three cells for each additional 
mile. 

It does not take long to learn to operate a telegraph in- 
strument. First one must learn to make the letters by the 
Morse code. This is a system of dots, dashes, and spaces 
to indicate the various letters of the alphabet. 

152 



THE TELEGRAPH 

The Morse Telegraph Code 

\BCDEF GH 

_ __ • • • • • • — • • • • — • — ^ * • • • 

J K L M N O P 

Q R S T U V W 

, li— • • • • • • • — • • — • • • -^ • — ■ 

X Y Z & I 



To make a dot press the key down and release it instantly. 
The sounder will then produce two clicks, one when the keeper 
hits the magnet contact-point and another when the spring 
brings it up sharp against the other point. These two 
cUcks very close together constitute a dot in the code. It is 
plain that the clicks themselves do not make the dots and 
dashes, but the interval of time between the clicks is counted. 
A dash is but a longer interval between the two chcks. A 
space is a pause. The dash has a length of three dots. The 
space between letters is three dots and the space between 
words is six dots. 

I The letter C is two dots, a space, and a dot. To make this 

I letter on the key you make a dot, then a dot, then wait an 

I instant, and then make the last dot. 

! With a little practice the entire alphabet can be mastered 

1 so that any letter can be made without serious thought. 

I In fact, it soon becomes as automatic as writing. 

1 153 



HARPER'S BEGINNING ELECTRICITY 

Some find it easier to learn to "read" the message from 
the sounder than to learn to send, and others are the reverse. 
When one has learned to make the letters on the key it soon 
becomes easy to recognize them as they click forth from the 
sounder. 

Beginners should always make every letter slow and dis- 
tinct, with a short interval between each word. If the Hs- 
tener fails to understand he has only to open his key and 
answer with a series of dots, which signifies that he has 
failed to catch the last word. In practice it is not necessary 
to spell out every word. Common abbreviations like ans 
for answer, and in. for inches, are always used in telegraphy, 
and many are added thereto at the will of the operator. 

Harper s Wireless Book, by A. Hyatt Verrill, is a new and 
complete explanation of the wireless use of electricity. 



Chapter XVII 

THE TELEPHONE 

TELE is from the Greek tele, meaning far. Phone is from 
the same language, meaning sound. 

The transmission of speech by wire has been known for 
many years. Very early experiments with sound-waves 
proved that the voice could be reproduced at a distance by 
using a tightly stretched wire with a diaphragm, or drum- 
head, at each end. In 1837 it was noticed that a bar of 
soft iron gave out certain musical vibrations whenever an 
electrical current was sent through it. Bourseul predicted 
the telephone in 1854. The first telephones were designed 
to reproduce musical notes. It was not until 1874 that 
Elisha Gray began his interesting experiments in Chicago, 
and Alexander Graham Bell took up the study of the tele- 
phone in Boston. Gray and Bell filed their applications for 
patent on the same day. Bell arrived at the Patent Office 
one hour before Gray, and this gave him the preference. 
Gray contested Bell's claims, but a compromise was eflPected. 

The first telephone was no more than a toy, and the 
public paid no attention to it until the Emperor of Brazil 
picked it up at the great Philadelphia Centennial in 1876 
and was astonished to hear it talk. 

Sound-Waves Are Not Transmitted 

It is not actually a human voice which we hear when we 
use the telephone. It is merely an accurate reproduction 

155 



HARPER'S BEGINNING ELECTRICITY 

of that voice faithfully copied, carried, and repeated by 
electricity. 

If the telephone was but a medium to transmit sound- 
waves it would be tar, mdeed, from the convenience it is now. 
Sound travels ver}' slowl}- when compared with electricity 
or light, as the speed of sound-waves through the air is only 
about 1,090 feet a second. It is nine hundred and seventy 
miles from Xew 1 ork to Chicago, or 5,102,200 feet; there- 
fore it would take a sound-wave 5,681 seconds to travel the 
distance, supposing, of course, it were possible for sound to 
travel that distance and be audible. This equals seventv- 
eight minutes, or an hour and eighteen minutes. Therefore, 
if you said ''Hello" in this end of a sound-wave hne you 
would have to wait two hours and thirt}'-six minutes to get 
an answer from Chicago. 

Sound-waves can be likened to waves in a mill-pond when 
a stone disturbs the calm water. The waves start out in 
complete circles and run slower and flatter until the}' fade 
away entirely or run up against something. The human 
voice is audible in ordinar}' conversation for only a few yards, 
and the lusty voice of a strong man on a still morning can 
be heard less than a mile. Giant siren whistles can be heard 
m still air for about three miles, and much farther than that 
if the wind is blowing from the whistle to the listener — or 
shorter if conditions are reversed. Cannon and thunder 
can be heard the farthest. The speaking-tube is the only 
telephone which actually transmits sound-waves in the air. 
Sound will also travel through metal, water, gases, and almost 
any other solid or gaseous substance, and is greatlr muiSed 
by soft hbers such as wool, cotton, sawdust, dirt, etc. Sound- 
waves can also be transmitted in a crude way through wire, 
and short-line telephones have been constructed after this 
plan. 

156 



THE TELEPHONE 

In some respects sound-waves resemble light-waves. They 
!! may be reflected, as every one who has listened to an echo 
I can testify, refracted, or bent, out of their natural course, 
I or sent through an open window or a hole in a building; 
I but they travel very slowly, because their way through the 
j air is so difficult and they soon lose their force and die out. 

How the Voice Is Transmitted 

The human voice is produced mechanically. Edison 
! proved this when he made a machine out of wood, wax, and 
I iron which would talk. Words are nothing but vibrations 
in the air produced by similar vibrations of the cords in the 
larynx; therefore a common metal disk can be made to 
make these same vibrations and actually repeat the human 
voice. 

This is the secret of the telephone. 

Without electricity it would be quite impossible to talk 
from New York to Chicago or Denver, as we can very easily 
do to-day. Sound-waves would not carry outside the great 
metropolis. What really happens is as follows: The voice 
causes a very thin metal diaphragm in the telephone to vi- 
brate in sympathy with the voice. This vibrating-disk 
oscillates in front of an electromagnet which sends little 
currents of electricity along the wires, which are in turn 
repeated by a similar magnet on the other end of the line. 
This second magnet, influenced by the electricity from the 
I first diaphragm, causes the diaphragm in the receiver to 
i vibrate just as the first one did, and of course in vibrating it 
I repeats in Chicago what was said to it in New York in exactly 
; the same tone. 

I Electricity travels at a speed of 186,000 miles a second. 
j This is so nearly instantaneous that it can be measured 

I 157 

i 



HARPER'S BEGINNING ELECTRICITY 

only with the most dehcate instruments. The time it takes 
electricity, carrying the human voice, to go from New York 
to Chicago, is so infinitesimally small that it can hardly be 
recorded in comprehensive figures. Therefore, the modern '' 
telephone is nearly instantaneous. 

Telephone Parts 

The principal parts of the telephone are the receiver, which ' 
receives and transforms the electrical waves into the sound- 
waves; the diaphragm, a thin disk of iron, which vibrates 
before the magnet; and the transmitter, which changes the 
sound-vibrations into electrical impulses and sends them to 
the other end of the wire. In long hnes a number of attach- 
ments have been added to perfect the apparatus. 

A simple telephone, which will work exceedingly well for 
short lines, can be easil}^ constructed. In making such a 
telephone any one can very easily learn the rudimentary 
principles of this wonderful apparatus. 

Instruments for a telephone line must be made in dupli- 
cate, so there will be one for each end of the line. For a 
simple telephone the receiver and the transmitter can be com- 
bined in one. The same instrument is used for both speak- 
ing and Hstening purposes. 



The Simplest Electric Telephone 

The following instructions are for building a single in- 
strument, and two must be made to be of any service. 

No batteries are necessary for this simple telephone line. 
Make a good permanent bar-magnet four inches long and 
three-eighths of an inch in diameter. Use round iron, and 
see that the steel is well magnetized. On the north-pole end 

. 158 



I 



THE TELEPHONE 

of this magnet fit two thin disks of wood one inch in diameter 
' and one-half inch apart to form a spool. Wind this spool 
j very carefully with fine insulated copper wire, No. 36, taking 
j care to leave ends about a foot long for connecting to the 
line (Fig. i). This will be the magnet and coil for the 
I telephone. 

I The permanent magnet with its coil of fine wire is the 

principal part of this telephone. It must be protected by 

i mounting it in a stick of hardwood six inches long and two 

I inches in diameter. Place the stick in a vise and bore a 

' straight hole in the exact center of it with an inch bit. 

i Sink the hole just one inch. Remove the inch bit and 

I replace it with a three-eighth-inch bit. Continue the hole 

through the entire length of the stick. Midway down the 

stick sink a smaller hole for a set-screw. 

I If this work is done neatly it will be found that the mag- 
net will easily drop down inside the stick until it is com- 
. pletely protected. Prepare two small holes for the wire 
I terminals so they can be brought outside the case (Fig. 2). 
I It is not necessary that this case be round, although it 
I will look better so. A square piece of wood is easier to 
I work, and will answer just as well. When finished the mag- 
net should be adjusted until it protrudes just a little beyond 
the end of the stick. Then it should be fastened firmly in 
place with a set-screw as indicated. 

I The Vibrating-Armature 

j The vibrating-disk can be made from an old tintype, or 
I a thin piece of tin. From either of these cut a circular disk 
I two and one-quarter inches in diameter. The metal can 
j be marked with a compass and cut with a pair of shears. 
I This disk must be smoothed out and mounted in a wooden 
I 159 



HARPER'S BEGINNING ELECTRICITY 



I 



frame just in front of the magnet head. This is best accom- ' 
plished by sawing out two wooden disks three and one-half' 
inches in diameter and half an inch thick. A two-inch hole I 
should be bored in the center of each disk. A little device i 
called an "extension-bit" is best for this work, as it is least i 
apt to crack the wood. Well-seasoned hardwood should be | 
used, as it is not so liable to crack and splinter (Fig. 3). |, 
Cut two washers out of cardboard three inches in diam- i 
eter and with a two-inch hole. Place the metal disk be- ! 
tween the cardboard washers in the center of the two pieces I 




Fig* 3 

of wood and fasten firmly together with screws. Holes ^ 
should be bored for the screws, using a bit just a trifle 
smaller than the screw-threads, and countersinking for the |^ 
heads so they will be even with the surface of the wood. 

Care should be taken in adjusting the metal disk to see 
that it is firmly caught along its entire edge by the pressure : 
of the wooden disks. 

The spool end of the permanent magnet should be smeared 

1 60 



THE TELEPHONE 



I around the outer edge with a Httle glue and inserted in the 
I disk a quarter of an inch. Do not push it in any farther, 
|or it will touch the diaphragm. When it has thoroughly 
Idried, the magnet should be adjusted until it almost touches 
jthe metal diaphragm and yet does nor quite do so. This 
,can be easily done by releasing the set-screw and pushing 
jthe magnet up until it just touches the diaphragm, and then 
jallowing it to fall back the thickness of a bit of writing- 
ipaper. Then fasten it firmly in place with the set-screw 

l(Fig. 4)- 

j The terminal wires should be brought down the handle 
[in shallow grooves to binding-screws at the base. The 
Ihandle can then be wrapped with bicycle tape, or heavy 
wrapping-paper glued in place, taking care to leave the set- 
screw clear for any readjustment that may be necessary. 
I When two of these instruments have been made it is 
Ibnly necessary to attach long insulated wires to the terminals 
and they are ready for use. No batteries are required. 
iiThe wires should be carefully insulated. It will be found 
j|that these instruments, when adjusted as they should be, 
'will be serviceable for a considerable distance. But for 
onger distances a different type of telephone, using battery 
:urrents, will have to be used. 

How the Telephone Works 

The action of the telephone made as above is very simple. 
The metal disk vibrates in accordance with the vibrations 
)f the voice. This disk, acting as an armature before the 
bole of the permanent magnet, sets up corresponding pulsat- 
ing currents in the spool of insulated wire about the magnet. 
These electrical pulsations pass along the wire to the other 
instrument, where they attract the other metal disk in the 

i6i 



HARPER'S BEGINNING ELECTRICITY 

same way, causing it to vibrate and thus reproduce the i^ 
voice. Of course, the voice will be weaker as the wires 
offer resistance to the passage of this feeble current. The 
farther the instruments are apart the weaker the voices will 
be, until the instruments are no longer serviceable. 

These instruments should be installed on a metaUic cir- 
cuit, i! 

This Hne provides no means of calling one to the tele- 
phone. It should also be equipped with an electric buzzer, 
or a bell, attached to the Hne behind the telephone instru- 
ments. This will require a single dry battery at each end, 
a push-button, and a buzzer. 

The manner of connecting this call system is best illus- 
trated in Fig. 5. 

For longer lines the telephone instruments should be pur- 
chased. Complete receivers and transmitters can be bought 
cheaper than they can be made. 

Batteries for the Telephone 

Telephone Unes cannot be operated over any consider-:^ 
able distance without batteries. For this work the dry-cell,ii 
or open-circuity battery is suitable. The battery itself doesi 
not give enough electromotive force to send a current ovetj, 
a long Une of considerable resistance. It must be associated 
with an induction-coil. Telephone coils are not large enough 
for sparking purposes, and their use is merely to raise the^ 
voltage of the battery current to overcome the Une resistance., 

The manner of connecting up the telephone instruments 
with the battery and coil is shown in the sketch (Fig. 6). 

Simple as it looks, a modern telephone line, for long-dis- 
tance service, is really very complicated and hard to under- 
stand. Over short lines magnetism is not necessary. Tht 

162 



THE TELEPHONE 



\^ 



® PUSH BUTTON 



BATTERY 



Fig. 5 




PRIMARY COIL SECOOARY COIL LINE 



31 



LINE 



BATTERY 

Fig. 6 






3 RECEIVER 



vibrations of the voice will travel over a taut wire. For 
longer service a magnet and coil are required. For still 
longer service batteries, induction-coils, and dynamos are 
utilized. The principal parts of a modern telephone are 
the transmitter, the receiver, induction-coil, bell, batteries, 
line, switch, and Hghtning arrester. 

The first telephones used a single transmitter-receiver at 
each end of the hne. Now both the transmitter and the re- 
ceiver are used. The receiver is a very delicate instrument? 
as it must communicate the weak line impulses to the vi- 
brating-diaphragm. With the modern transmitter the ordi- 
nary tone of voice can be heard over hundreds of miles. 

This is but the beginning of the study of the telephone. 
It is a complete profession in itself, and, as a rule, is kept 
apart from regular electrical work. The telephone system 

11 163 



HARPER^S BEGINNING ELECTRICITY 

of a large cit}', with its thousands of miles of wires and 
cables, both above and under ground, is a wonderful under- 
taking. The telephones are all controlled from a central 
office, where girls sit before long switchboards making the 
necessary connections in answer to the calls. Current for 
the lines is supplied from storage batteries. Current for 
ringing is supplied by d_vnamos. When the telephone re- 
ceiver in any home or office is hfted from its rest a tiny 
light flashes on the switchboard before the operator in the 
central office, so that she knows you are listening. She 
asks what number }'ou want, and when 3^ou tell her, she 
connects you with that number on the switchboard with a 
long flexible cord and plug. She calls the part}' by ringing 
a bell. When the receiver is hung up the signal light dis- 
appears and the operator removes the connection. 

It is entireh' possible to use telephone and telegraph in- 
struments on the same line without conflicting. This is 
the regular practice along some railroad lines. 

The wireless telephone has proven its possibilities, and 
doubtless will be in regular commercial operation within a. 
few years. Messages have already been exchanged over 
considerable distances. 



Chapter XVIII 

I DYNAMIC ELECTRICITY 

ONLY for the sake of convenience is electricity divided 
into three parts — static, galvanic, and dynamic. 
In reahty all three are very closely related, if not the 
same. No one knows the exact relationship, no one can 
I explain why they seem to differ in some respects and are 
I exactly alike in many other ways. 
I Static electricity is produced by friction. 
I Galvanic electricity is generated by chemical action. 

And dynamic electricity is the product of magnetism and 
induction. 

Now it should be written here that it is not certain 
that any of these methods actually produce electricity. But 
they do produce electromotive force. When we say that a 
battery produces electricity it should be interpreted in its 
broadest sense, the same as when we say a lamp produces 
Hght. The lamp really produces a wave -motion which, 
falling upon the delicate nerves of the eye, gives us the sensa- 
jtion known as light. 

It is doubtful if any of the above processes actually pro- 
jduce electricity. The probabilities are that they merely 
jraise the electrical potential or voltage, the same way a 
Ipump lifts water. This potential will flow back to its level, 
land in so doing will perform various tasks, just as falling 
jwater will do a certain amount of work in flowing back to 
the level of the sea. 
I 165 



HARPER'S BEGINNING ELECTRICITY 

Dynamic electricity is the result of mechanical energy 
acting on magnets. 

The Discovery of Dynamic Electricity 



During those early experiments with induction it was dis 
covered that if a loop of wire was passed between the poles 
of a permanent magnet a current of electricity was caused 
in the wire. It did not require much imagination to see 
that if the loop of wire was mounted on an axis, so it could 
be made to constantly cut the lines of force between the 
magnetic poles, the current would be practically contin- 
uous. A device was made to whirl several loops of wire 
between magnetic poles. The current generated in these 
loops was carried to brass plates fixed to opposite sides of 
the rotating axle and insulated from each other. The cur- 
rent was picked off from these plates by two fixed springs 
pressing against them. 

This was the first machine to generate a continuous flow 
of electricity by mechanical energy. It was called a 
magneto-electric machine. 

Electric generators which employ permanent magnets for 
the field are still called magnetos. 

Siemens made a long bobbin by winding copper wire 
lengthwise on a soft-iron shaft. This bobbin he called an 
armature, and so mounted it in a frame that it could be 
rotated between the poles of powerful permanent magnets. 

An electric current was induced in each loop of wire as 
it cut the lines of force between the poles of the magnets. 
This current flowed to the axis of the armature shaft, where 
it was collected on a split brass ring called a commutator. 
The word commute means to change or alter. A commutator 
is a little device to change or alter the direction of the 

1 66 

1 



\ 



DYNAMIC ELECTRICITY 



current flowing first one way, then the other, in the armature 
' coils, so that it issues from the dynamo always in one 

direction. 
I The development of the magneto-electric machine was 
slow. All the early students of electricity used permanent 
magnets in their machines. Finally some one hit upon the 
I plan of using an electromagnet in place of the permanent 
' magnets. In this way the size of the generator would be 
unHmited. But first a way had to be provided for sending 
a current through the coils of the electromagnet, otherwise 
it would have no magnetic properties. This was accom- 
plished by mounting a small magneto-electric machine, 
utilizing permanent magnets, on top of the electromagnet 
for exciting or magnetizing it. 

It was soon found that the ** exciter" could be done away 
with entirely. The electromagnet does not lose all its mag- 
netism when a current ceases to flow through its coils. A 
very little remains. This is called residual or resident mag- 
netism. This magnetism can be used to excite the electro- 
magnet, providing the magnet coils are placed within the 
circuit from the armature. 

With the success of the electromagnet in the construction 
of dynamos all permanent magnets were discarded. These 
machines were called dynamo-electric machines, which was 
soon shortened to dynamos, and of later years they have 
been known as generators, which is the better word. 

Working -Parts of the Dynamo 

The electromagnet coils soon came to be known as t\\Q field- 
coils, and later as the field. 

The rotating part is still called the armature. 

The device to direct the current from the revolving loops 

167 



HARPER'S BEGINNING ELECTRICITY 

of the armature and send it over the line is known as the 
commutator. 

The springs which press against the commutator-bars are 
the brushes, because they somewhat resemble a brush. 

The dynamo, or generator, does not create electricity. ; 
It simply imparts energy to it. The electromotive force is i 
raised from a lower potential to a higher potential by the re- 
volving coils, just as water is raised by a pump. The cur- ' 
rent generated in this way will flow back from a higher 
to a lower potential through the circuit, just as the water 
will flow back to the source from whence it was lifted by 
the pump. ■ 

When the armature coils are moved in the magnetic field, ' 
by mechanical energy, the conducting-coils cut the lines of ' 
force, and electricity is induced in the armature-winding. 
It requires power to move this armature across the lines 
of force, as the attraction of the magnetic poles has to be 
overcome. The more current taken from the generator, the 
more mechanical energy required to rotate the armature. 

There are two kinds of generators in common use, the 
direct-current generator and the alternating-current generator, i 

In the direct-current generator the current always flows ' 
in one direction over the circuit. This is accomphshed by i 
the commutator. 

In the alternating-current generator solid rings replace the 
commutator, and the current surges back and forth over the | 
line, first one way and then the other. 



How Electrical Energy Is Produced from Coal 



i 



It is interesting to follow the many changes involved in 
producing electrical energy from the stored-up energy of 
coal in a modern electric-hght plant. 

i68 








'"^ ^B^^^^^^ 



STATOR OF ALTERNATING-CURRENT 
GENERATOR, SHOWING WINDINGS 




ROTOR OF ALTERNATING-CURRENT GENERATOR. CONDITIONS BEING RE- 
VERSED IN THIS TYPE OF GENERATOR. THIS SHOWS THE FIELD-COILS 




DIRECT- CURRENT, I25-VOLT GENERATOR, 
SHOWING FIELD STRUCTURE AND ARMATURE 



DYNAMIC ELECTRICITY 

Coal is the energy of the sun stored up in the form of 
carbon. This carbon is fed into large furnaces, where it is 
made to combine with the oxygen in the air. This releases 
the energy of the coal in the form of heat. The furnace is 
built directly under a boiler designed so this heat-energy 
comes into immediate contact with a great many steel tubes 
filled with water. About seventy per cent, of this heat-energy 
is transmitted to the water. The rest is wasted in useless 
radiation up the smoke-stack or out into the power-house. 

Water has the property of rapidly absorbing heat-energy. 
This changes the liquid mto a powerful gas capable of great 
expansion. In this form, still very hot and under great 
pressure, it is sent through steam-pipes to the steam-tur- 
bines. Here most of the expansive energy of the steam is 
imparted to the rotating-planes of the turbine, causing them 
to move. The energy of the coal is now changed to mechani- 
cal energy and made to whirl the rotating part of a powerful 
electric generator, where it is changed into electrical energy. 

Unfortunately, only about seventeen per cent, of the heat- 
energy which is represented in the steam from the boilers 
can be changed into electrical energy. The reason for this 
serious loss is the nature of steam itself, which will not give 
up the greater part of its heat-energy until it changes back 
into water, at which time it is not available in modern engines. 

The electric current generated in the machine is led 
through insulated cables to the near-by switchboard. From 
this point it is directed over the numerous distribution 
wires to the points where needed for light, heat, or power. 

Two Forms of Current 

All electricity generated by mechanical energy is alter^ 
nating in its inception. At first this alternating current was 

171 



HARPER'S BEGINNING ELECTRICITY 

undesirable, and the commutator was devised which could 
be so connected to the alternating-current machine that the 
current would always flow one way. 

Alternating current, often abbreviated A. C, flows back 
and forth in the circuit instead of flowing continuously in 
one direction as direct current. Starting from zero, the 
current quickly reaches a maximum in one direction and 
then comes back to zero again, increasing to the maximum 
in the other direction and then back to zero again, as shown 
in Fig. I. 

In ordinary commercial alternating current there are about 
sixty of these cycles each second. An alternation is one- 



ZERO 




Fig.t 

half of a complete cycle. A current of sixty cycles per sec- 
ond will have one hundred and twenty alternations. 

The words cycles, frequency, and alternations are not used 
when speaking of direct current. 

Both alternating and direct current are measured the same. 
The unit of potential, or pressure, is the volt, and the ampere 
denotes the quantity. Both kinds of current have their 
uses. Alternating current has the widest field because of 
the strange fact that it can be easily transmitted long dis- 
tances over small conductors at high potential. Some of the 
largest power companies send alternating current several 
hundred miles over small copper wires at the enormous 
potential of 150,000 volts. It is practically impossible to 
raise the voltage, or potential, of direct current to this figure, 

172 



DYNAMIC ELECTRICITY 

so it cannot be economically transmitted over long distances. 
Alternating current is generally used for lighting houses, 
offices, and factories. It is also extensively used for power. 
I Direct current finds its greatest field of usefulness in street- 
; railway work, and for arc-Hghting in the public squares and 
streets. A chemical battery gives only direct current. 



Chapter XIX ji 

I" 

THE DYNAMO, OR GENERATOR 1 

THE great electrical industry practically dates from the 
invention and development of the d3mamo, or genera- 
tor. Batteries were too cumbersome and costly. Electri- 
city produced by mechanical energy made possible the 
street-railway, the modern electric light, the power-motor, 
and the thousand and one apphcations of this wonderful 
energ}^ so common to-dav. 

The dynamo, or generator, must always be provided with 
a source of energy. It must be connected to a water-wheel, 
a steam-engine, or some other source of power. It is merely 
a medmm of mechanical exchange. It takes the mechani- 
cal energy from the faUing water or the steam-engine and 
changes it into electrical energy. This change is not made 
without some loss. There is friction to overcome, and this j 
requires energy. i 

The generator must always consist of two essential parts : 
the field-magnets and the rotating-armature. Between 
the poles of these magnets flow the invisible magnetic rays. 
These lines of force flow out of the north pole and into the 
south pole. The armature is similar to an electromagnet. ^ 
It consists of a core of soft iron wound with loops of insulated -. 
copper wire. These loops must be at right angles to the 
lines of force and arranged so the armature can be rapidly 
whirled in the magnetic field. In this way the copper loops 

174 



THE DYNAMO, OR GENERATOR 

are made to cut, or break across, the lines of force at high 
speed. This cutting, or breaking, causes a current to be 
induced in the copper wire. 

Just how and why a current of electricity is induced in 
the armature loops when they cut the lines of force in the 
magnetic field no man can say. It cannot be explained so 
the ordinary student of electricity will understand. It is 
best to proceed without this knowledge, which is of little 

I practical value, and accept the fact that such a current is 

j produced. 

I The First Dynamo 

When Faraday had proven that electricity could be in- 
duced in a wire by moving it between the poles of a magnet, 
he set about to make the first magnetic generator. Fara- 
day's first machine was a very simple affair. Any one can 
make one in a few minutes and thus prove beyond a doubt 
that moving a good conductor within the lines of force 
between the poles of a magnet will cause a current of 
electricity to flow in the conductor. 

Faraday mounted a brass disk so it could be revolved on 
a crank-shaft between the poles of a permanent magnet, 
without actually touching them. A spring rubbed against 
the upper edge of the brass wheel. Another spring rubbed 
against the iron axle. These springs were connected to 
short wires which were attached to the galvanometer. 
When the crank was turned the springs conducted the elec- 
tricity to and from the wire circuit, and the galvanometer 
showed that a current was actually flowing in the wires 
(Fig. I). 

To Make an Experimental Dynamo 

If one desires to make a thorough test of the theory of 
the dynamo it is best to construct a more powerful machine 

175 



HARPER'S BEGINNING ELECTRICITY 



after the plan suggested by Gramme. In place of Fara- 
day's brass wheel Gramme used a soft-iron ring mounted 
on a groved wooden wheel. The ring is wound with regu- 
larly spaced loops of insulated copper wire. These loops 
are connected to pins driven in a circle around the axis of 
the wooden wheel. Brass collecting-springs rub against 




MAGNET 



BRASS DISK 

Fig.t 



GALVANOMETER 





TT H 




*. COILS 
IRON RING 



Fig. 2 



these pins from opposing sides. This wheel, when finished,^ 
is mounted so it can be rapidly turned above the poles of a 
powerful magnet. When the machine is in motion a strong 
current of electricit}^ is generated in the conducting-wires 

(Fig. 2). \ 

176 ! 



THE DYNAMO, OR GENERATOR 

If an iron ring is not available, one can be made by bend- 
ing a round bar of half-inch iron and soldering the joint. 
It can also be made of iron wire wound into a circular coil 
a half inch in thickness, with the two ends of the wire 
soldered. This ring, or coil, should be insulated with a 
layer of heavy paper or varnished linen cloth. The wooden 
wheel to hold the ring should be made in two parts, screwed 
together, otherwise it will be difficult to mount it securely. 
Copper wire is wound tightly about the ring at quarter-inch 
intervals. The ends should be soldered together. There 
should be an even number of loops, and every fourth loop 
should be connected to a pin with a bit of copper wire sol- 
dered to both loop and pin. Brass springs pressing on 
either side of this circle of pins conduct the current to the 
line. 

If the iron ring with its loops of wire be mounted so as 

to whirl very near the poles of a magnet, without actually 

touching them, a current of electricity will flow from the 

collector-pins over the short wire circuit. The deflection 

of the compass needle of the galvanometer will show the 

direction and strength of this current. However, this is 

j but a toy at best, and serves no purpose other than dem- 

! onstrating the principle of the dynamo. 

I Permanent magnets for the field were discarded many 

j years ago in favor of electromagnets. As an electromagnet 

j can be made any size with ever-increasing strength in pro- 

I portion to the iron and wire used, there is no limit to the 

j size of possible generators. The world's largest generator 

I of ten years ago is but a toy beside those being built to-day. 

j Perhaps these will seem small ten years from now. 

With powerful electromagnets for the field the develop- 
ment of the generator was very rapid. Any number of 
these magnetic poles could be arranged in the field, thus 

177 



HARPER'S BEGINNING ELECTRICITY 



t 



increasing the flow of current. The residual magnetism left 
in the field-coils is generally enough to start the flow of ' 
current as soon as the armature is revolved. Some of the 
larger machines have to be "excited" with a smaller gen- 
erator. 

The Secret of the Generator 

It is not hard to understand the process by which a current 
is produced by the dynamo. If a plain copper wire is bent 
into a rectangular loop and mounted on a wooden shaft, so 
it can be turned between the poles of a permanent magnet, 
electricity will be generated in the loop (Fig. 3). 

In this simple generator the invisible lines of magnetic 
force flow straight across from the north pole to the south 
pole of the magnets. When the wire loop is straight up 
and down it is said to be neutral^ and no current is produced, 
for at that instant it travels with the Hnes of force, and not 
across them. As the shaft is turned the top of the loop. 
No. I, begins to cut the lines of force in a downward stroke. 
These invisible ra3^s oppose this motion; they repulse the 
wire, and it requires force to drive the loop across the lines 
of force. At the same time the bottom of the loop, No. 2, 
begins to cut the lines in an upward stroke. This loop is [ 
likewise repulsed. The driving of these loops across the 
lines of force produces a flow of current in the loop by 
induction. This current runs out to the sliding contact- 
ring on the shaft, and thence over the circuit and back to 
the loop from the second contact-ring. 

When the loop has finished a half- revolution it again 
reaches the neutral point. But the top of the loop. No. I,' 
is now at the bottom, and No. 2 is now at the top. At the 
next half-revolution No. 2 cuts the lines of force in a down- 
ward stroke, and No. i in the upward stroke. This i$ 

178 



j THE DYNAMO, OR GENERATOR 

j exactly opposite of what occurred during the first half- 
I revolution, consequently a current is caused to flow in the 
{opposite direction over the circuit. For every complete 
j revolution of the copper loop two currents of electricity are 

I LINES OF FORCE 

X 



Fig. 3 




Fig. 4 

.generated and flow over the circuit in opposite directions. 
Phis kind of a generator is called a simple alternator, or 
ilternating-current generator. 

, If we now replace the contact-rings with a split ring, and 
.nsulate each half of this ring from the other, we can make 
.he current flow always in one direction. This split ring 
ijv^iU reverse the direction of the flow as often as the loops 
K wire reverse in turning. This spKt-ring collector is 
Jailed a commutator because it commutes, or changes, the 
firection of the flow (Fig. 4). 

.1 Because of the reversal of the direction of the current 
\Y the commutator this type of machine is called a direct- 
.^rrent generator, meaning that the current flows from it 

179 



HARPER'S BEGINNING ELECTRICITY 

always in one direction. This flow is not stead}^, like that 
from a battery, but pulsates, owing to the neutral points 
between the magnetic poles. These neutral points can be 
lessened by using a greater number of loops and by adjust- 
ing the commutator. Where a number of magnetic poles 
are used in the field, and many loops of wire in the armature, 
the current is reasonably steady. 

Small, home-made generators are of little service because 
they must be driven by some form of power. They must 
be turned by hand, by a small water-wheel, or other source 
of power. When the power ceases the current ceases. 
Such a generator can be used to supply current for small 
motors, miniature lights, etc., but they are not as good as 
batteries. 

Making a Small Generator 

The simplest form of a generator to build is the bipolar, 
or two-pole, direct-current generator. This machine can 
be built in any size, from the toy of a few inches high to 
one of several horse-power. The following is a description 
of such a generator six inches high and five inches wide. 
This generator consists of three main parts — the electro- 
magnet, the armature, and the commutator. 

The core of the electromagnet is made up of three parts — 
the soft-iron core, the magnet-heads, and the yoke. The 
cores are of soft iron each three-quarters of an inch in di- 
ameter, and three and one-half inches long, inside of the 
threads. The magnet-heads are of soft iron, hollowed out 
for the armature, three inches wide, two inches thick, and 
one and one-half inches wide. Both heads are bored and 
threaded for the round iron cores and the base screw. The 
yoke is five inches long, one inch wide, and half an inch 
thick, also drilled and threaded for the cores (Fig. 5). 

180 



J 



THE DYNAMO, OR GENERATOR 




If desired, this frame can be made of pieces of sheet-iron 
cut after the pattern shown and bolted together (Fig. 6). 

The armature is also of soft iron in the form of a cube 
three inches long and two inches in diameter. It is drilled 
for the shaft and slotted for the coil (Fig 7). 

Winding the Field-Coils 



After the frame for the electromagnet is made it should 
be wound with cloth where the field-coils are to be placed 
j and thoroughly varnished with shellac. Adjust two wooden 
I disks to keep the field-coils in place, and then lay on seven 
j layers of No. 16 cotton-covered wire. Be careful to wind 
I both sides of the magnet in the same direction. 
I The armature is wound with five layers of No. 18 silk- 
! covered wire laid firmly in the slot provided for it. The 
I finished armature should be somewhat smaller than the 
I bore in the frame, so it can be revolved without actually 
I rubbing the magnet-heads (Fig. 8). 
i 12 181 



HARPER'S BEGINNING ELECTRICITY 

A split-ring commutator is used. This is made of a 
brass ferrule mounted on one end of the shaft. This ferrule 
must be insulated from the shaft. This can be done in 
many ways. The best way is to sHp it over a hard-rubber 
cyhnder which has been tightly shrunk on the shaft close 
to the armature. The ferrule is fastened in place from op- 
posite sides and then filed or sawed in two. One end of the 
armature wire is soldered to the top half of the spHt ring fc 
and the other end to the remaining half, as per diagram 

(Fig. 9)- 
The armature shaft is mounted so the armature can be 




Fig. 6 




o o o oo o 
o o o ooo 
oo o ooo 
o o o o o o 



o o o o o 
o oooo 
o o ooo 
o o ooo 

Fig. 8 




182 



THE DYNAMO, OR GENERATOR 



turned from the pulley without rubbing against the magnet- 
heads. Any imperfections can be corrected with a file 
until it turns without contact. 

The commutator-brushes are two brass springs adjusted 



COMMUTATOR 



PULLEY 




Fig.tt 



Fig. 12 



Fig. t3 



Fig. t4 



on opposite sides of the shaft so as to press against the split 
ring (Fig. lo). 

[ Connecting the Generator to the Circuit 

I The generator should be connected up in series. This 
I means that the current should flow from the armature 
! through the electromagnet and out over the wire circuit, as 
I illustrated in Figs, ii, 12, 13, and 14, in which are shown 
I generators of various types and the manner of exciting field. 

! ' 1B3 



HARPER'S BEGINNING ELECTRICITY 

Fig. II represents a generator the held-magnets of which 
are excited by a separate batten'. Fig. 12 is the diagram 
of a " series "-wound d^Tiamo. When the armature is 
driven at high speed the current flows through the field- 
magnets, which become self-exciting. The type shown in 
Fig. 13 is known as "shunt "-wound. The held-magnet 
coils and the external resistance are in parallel, or shunt 
each other, instead of in series. In Fig. 14 a "compound- 
wound" d}-namo is shown. It is a combination of the 
series and the shunt machine. 

In these hgure-drawings F represents the held, A thr 
armature, C the commutators, B and BB the brushes. 

To operate the generator when it is complete the current 
of three dry cells is first sent through the electromagnet. 
Ejiough magnetism will remain after the cells are taken 
away to start the machine. As soon as the current begins 
to flow through the armature coils the magnet will be 
sufficiently excited. This type of dynamo must be turned 
verv' rapidly. To accomplish this the small pulley on the 
armature shaft should be belted to a large twelve-inch 
pulley which can be operated by hand. 

Larger generators will require castings for the electro- 
magnet and armature cores. 

The direct-current generator of this t>'pe can easil}- be 
made into an alternating machine by removing the split 
commutator and replacing it with double rings. 

In the A. C. machine an alternating current is produced 
in the armature. It flows backward and forward over the 
circuit each time the coils pass the poles. In the case of 
the two-pole machine the current completes one cycle each 
time the armature completes a revolution. If the field 
consisted of eight poles, four pair, there would be four cycles 
for each complete revolution. 

184. 







ALTERNATING-CURRENT GENERATOR WITH SMALL GENERATOR MOUNTED 
ON THE END OF THE ROTOR SHAFT FOR EXCITING THE GENERATOR FILED 




TRANSFORMER, SHOWING MECHANISM AND IRON TANK. THE TRANS- 
FORMING-COILS ARE SUBMERGED IN OIL FOR INSULATING PURPOSES 



THE DYNAMO, OR GENERATOR 

Several Kinds of Generators 

This type of A. C. generator is called a "single-phase" 
generator. An A. C. generator may be built with two in- 
dependent sets of coils, with one set lying between the 
other. Each set is connected to its own pair of collector- 
rings. In this way two alternating currents are produced 
by the same machine. One current is rising when the 
other is falling, and falling as the other is rising. In this 
machine a "two-phase" current is produced. Three or 
more coils may be used, and "three-phase" or polyphase 
current produced. Poly means many. 

Electric generators are made in all sizes, from the tiny 
fellow no larger than an ink bottle to single units of more 
than 30,000 horse-power. There are many different kinds, 
generating a great variety of current. Some produce a cur- 
rent of high voltage and correspondingly low amperage. 
Others give a current of low voltage and high amperage. 
Generators are designed especially for incandescent lighting, 
for arc-lighting, for railway work, for electric heating, and 
for various other purposes. It is possible to vary the volt- 
age and amperage of a generator by simply changing the 
winding and the speed. 

Not one entire book, but many large books would be re- 
quired to describe all the different types of electric genera- 
tors now in use. After one has mastered the principles of 
the common bi-polar, direct-current machine it is easy 
enough to study out the workings of any generator. 

Alternating current, regardless of whether it be single or 
polyphase, has a distinct advantage over direct current 
in commercial service because it can be easily transformed 
from one pressure, or voltage, to another. This character- 
istic is entirely due to its pulsating nature. 

187 



HARPER'S BEGINNING ELECTRICITY 

The Transformer, Which Raises or Lowers the Voltage 

The apparatus used for raising or lowering the voltage 
of an alternating current is the "transformer," so called 
because it really transforms the voltage. 




CORE 



SECONDARY 
COIL 



Fig. /5 

The transformer contains no moving parts. It is very 
difficult to explain the actions of this device. It is merely 
an adaptation of the induction-coil principle on a larger scale 
(Fig. i). The current sent pulsating through the primary 
coils are induced, with increased or decreased voltage as 
desired, in the secondary coils. In the accompanying illus- 
trations the principle of the transformer and the mechanism 
and iron tank of a transformer are shown. The transform- 
ing-coils are submerged in oil for insulating purposes. 

Transformers have been built for laboratory work which 
would raise the voltage of the primary current to 500,000 
volts. The spark-coil for the ignition of gasolene-engines 
in automobiles is a miniature transformer. 



Chapter XX 

THE ELECTRIC MOTOR 

MOTOR is from the Latin motus, to move. 
An electric motor is a device to change electrical 
energy into mechanical energ}^ 

In the modern home or factory electricity is always "on 
tap," just the same as the water-supply. You turn the 
faucet and draw as much water as desired; you press the 
button or turn the switch and draw out as much electricity 
as needed for light, heat, or power. 

The source of power in a motor is always a mystery to 
the observer. The armature can be seen revolving at a high 
rate of speed, but nothing, apparently, drives it. Indeed, 
the force which whirls the motor is quite invisible. It is 
impossible to see it, but we know that it is there. 

Why the Motor Whirls 

By way of explanation take the direct-current, bi-polar 
motor, which, as its name implies, consists of a single field- 
magnet of two poles. The magnetizing-coils of this field- 
magnet are placed in a solid frame with the polar ends 
facing, leaving a suitable space between known as the 
magnetic -field, in which the armature revolves. When 
an electric current is passed through the magnetizing-coils 
of the field a powerful magnet is produced of which one end 
is the north, or positive, pole, and the other and opposite 

l8q 



HARPER'S BEGINNING ELECTRICITY 

end the south, or negative, pole. The lines of invisible 
magnetic force extend across between these poles. If a 
copper wire carrj'ing an electric current was passed down- 
ward straight between these two poles, cutting the lines of 
magnetic force at right angles, a mysterious power would 
force the wire back to the top of the magnetic Hnes. The 
armature, which rotates between the poles of the field-mag- 
net in a motor, is nothing more than a series of coils of wire 
through which an electric current is passing. Those coils 
which are at the bottom of the lines of magnetic force 
between the poles of the field-magnet are being forced up- 
ward on the posit ice side and downward on the negative side. 
This motion would stop as soon as the armature coils ad- 
justed themselves in accordance with the lines of magnetic 
force if it was not for the coryuniitator. The duty of the 
commutator, which is a divided ring of insulated copper 
fastened to the axle of the armature, is periodically to re- 
verse the current passing through the armature coils so 
they never adjust themselves to the magnetic force flowing 
between the poles of the field-magnet. Xo matter how fast 
or slow the motor runs, as the armature revolves, the 
"brushes," which feed the current to the armature coils by 
contact with the split surface of the revolving commutator, 
reverse the current in time to keep the strange magnetic 
force always exerting its invisible power to drag one side 
of the armature up and to force the other side down. This 
force gives the armature continuous motion and power. 
Increasing the electric current in the armature coils in- 
creases the power of this magnetic ^^pull," and the horse- 
power of the motor grows accordingly. 

A glance at the motor running so quietly, and doing so 
much work for so small a body, will reveal all these facts. 
The field-magnets can be readily seen. It takes but a f 

I go 



THE ELECTRIC MOTOR 

little imagination to realize the lines of magnetic force ex- 
tending between the opposing poles. In the surface of the 
armature, when the motor is stopped, the coils can be seen 
embedded in slots. These coils are made of insulated wire 
in the smaller motors, and heavy insulated copper strips 
in the larger machines. After these things are noted it is 
easy to understand the powerful magnetic force which is 
pulling continually to adjust the coils in the armature to 
a certain position and then, just as the task seems to be 
completed, the little revolving commutator has reversed 
the current and the work has to be done all over again. 
And so on, minute after minute, day after day, year after 
year, the magnets are working to set the lines of force right 
according to nature's own irrevocable laws, and man keeps 
them ever opposed and utilizes the energy expended to turn 
the wheels of his industries, drive railroad-trains, and to 
supply him with power for everything. 

Birth of the Motor 

The first commercial electric motors were made by 
Thomas Davenport, a Vermont blacksmith, about 1834. 
Faraday and others had already discovered the principle 
of the electric motor, although their first motors were mere 
toys. But it was Davenport who first saw the possibiHties 
of the motor to drive vehicles and machinery. His model 
electric railway was exhibited in Springfield, Massachusetts, 
in 1835. I^ ^^^ ^^ perfected over a hundred different types 
of electric motors. But Davenport was fifty years ahead 
of his time. The electric motor could not be commercially 
a success until the dynamo, or generator, was perfected. 

The electric motor was reborn at the Paris Exposition. 
One of the dynamos on exhibition threw off the belt, and, 

191 



HARPER'S BEGINNING ELECTRICITY 

to the surprise of every one, continued to run. All efforts | 
to stop it failed. Then and there it was discovered that a 
dynamo, or generator, is also a motor. In fact a motor can f 
be used as a dynamo, or a dynamo as a motor. Up to the 
accidental discovery of the fact that there is Httle difference ? 
between a dynamo and a motor it was thought that a motor 
had to be radically different from a dynamo. 

Toy Motors 

When a magnet attracts a bit of soft iron and causes the 
iron to jump toward its magnetized poles, motion has been 
produced by electricity. If the piece of soft iron is sus- 
pended on a string before an electromagnet it will swing 
toward the magnet whenever a current is sent through the 
magnetizing-coils. When the current is stopped the iron 
will swing away from the magnet. With a little device to 
"make" and "break" the circuit this motion can be made 1^ 
continuous. The vibrations of an electric bell are pro- 1' 
duced in this way. A little spring "makes" and "breaks"! 
the circuit. 

Toy electric motors are sometimes made which utilize 
the attraction of an electromagnet on a "make "-and- b 
"break" circuit to impart motion to a shaft and wheel. 
These engines are made on the same plan as an electric bell, 
or the vibrator of an induction-coil. The backward and 
forward motion of the spring-armature is used to drive ai 
tiny crank-shaft and balance-wheel (Fig. i). ! 

The crank-shaft (CS) is made of brass wire, with the cranks 
itself adjusted to the stroke of the armature. The con-^i 
nection-rod (CR) is pivoted to the armature and the crank-' 
shaft. The balance-wheel (BW) is soldered to the crank-, 
shaft and mounted to turn freely in bearings. ; 

192 



THE ELECTRIC MOTOR 

The action of this toy engine is exactly the same as that 
of the vibrator. When the engine is connected to the 
battery the current flows through the coils of the electro- 
magnet (M M). The magnet pulls the armature down until 
it almost touches the magnet core. This breaks the cir- 
cuit, and the spring (S) throws the keeper back up, making 




Fig.t 

the connection anew. This operation is repeated with great 
rapidity, producing a loud humming noise. This recipro- 
cating motion of the armature is imparted to the connection- 
rod, and from that to the shaft by the crank. A Kttle 
adjustment of the terminal - screw may be necessary in 
starting the engine. 

The direct-current motor consists of an armature and 
a magnetic field, just the same as the D. C. generator. 
The armature is connected to the Hne circuit by means of 
a commutator, which reverses the direction of the current 
through the armature-windings at the proper time, so the 
armature is rotated continuously (Fig. 2). 



Different Types of Motors 

Direct-current motors may be either shunt, series, or 
compound wound, according to the method of exciting the 

193 



HARPER'S BEGINNING ELECTRICITY 



field-magnets. In the case of the shunt-wound motor a por- 
tion of the Hne current is shunted aside to excite the field. 
In a series motor all the hne current passes through both 
armature and field-coils, they being placed in series on the 
line. A compound motor is a combination of a shunt and 
series wound motor. (See Figs. 1 1, 12, 13, 14, Chapter XIX). 

In the beginning the direct-current motor had but two 
poles. Now they are made with several pairs of poles, de- 
pending upon the size of the motor and the work required 
(Fig. 3)- _ 

A very simple explanation of the direct-current motor is 
based upon the law that similar magnetic poles repel each 
other and opposite poles attract each other. Assuming that 
the north pole of the armature is traveling toward the south 





Fig. 2 



pole of the field, being attracted toward each other, then 
the south pole of the armature is also being drawn toward the »' 
north pole of the field. When these opposite poles reached : 
a position opposite each other the armature would cease 1: 
to turn. But, just as they are about adjusted, the Httle 
commutator on the armature axle changes the direction of 
the current flowing through the armature coils, and this 

194 




PARTS OF A THREE-QUARTER HORSE - POWER DIRECT-CUR- 
RENT MOTOR, SHOWING FRAME, FIELD-COILS, AND ARMATURE 




SMALL INDUCTION ALTERNATING - CURRENT 
MOTOR, SHOWING FRAME, STATOR, ROTOR, ETC. 



I 



I 



THE ELECTRIC MOTOR 

instantly reverses the poles. The poles being now alike, 
they repel each other, and each north pole is repelled by 
each north pole and attracted by the succeeding south pole. 
This operation is continuous, and the armature rotates as 
long as the current flows. 

In large direct -current motors the commutator-ring is 
split into a number of segments, or pieces, so that the polarity 
of the armature coils is reversed very frequently. This main- 
tains a very even and continuous rotation of the armature. 

In all high-voltage D. C. machines the fine wire of the 
armature coils must be protected from burning when start- 
ing the motor. A starting-box, or rheostat, is used for this 
purpose. This device puts enough resistance between the 
line and the motor to reduce the current at the start. As 
the motor speeds up this resistance is gradually removed 
until the full strength of the current is flowing. Rheostats 
are generally used for direct-current motors. 

Electric motors are made for both direct and alternating 
currents. Care should be taken to make, or purchase, only 
direct-current machines for D. C. fines, and only alternating- 
current motors for A. C. lines. Any attempt to operate an 
A.. C. motor on a D. C. line will fail, and vice versa. Motors 
are made for a certain voltage. For a iio-volt circuit a 
motor of that voltage should be used. If an attempt is 
made to operate a 20-volt motor on a iio-volt fine the 
motor will soon become hot and will be destroyed. 

The A. C. Motor 

The alternating-current motor is hard to understand and 
harder still to make. 

There are two classes of alternating-current motors : the 
induction motor and the synchronous motor. 

197 



HARPER'S BEGINNING ELECTRICITY 

The stationary part of an alternating-current motor is 
called the stator. The moving part is the rotor. 

The windings of the stator in a common induction motor 
are usually embedded in slots instead of being wound upon 
poles. The rotor consists of copper wire, as bars, laid into 
slots cut into an iron core. 

There are several ways of constructing toy motors. 
Once the principle of the electric motor is mastered it is quite 
easy to make a motor after individual designs and to suit 
the material in hand. 

A very good motor can be made by following the direc- 
tions given in a previous chapter for building a small gen- 
erator. This generator will operate as a motor if connected 
to five or six good battery cells. 

For large motors, of a quarter horse-power or more, cast- 
ings and machine work are necessary. Patterns for the 
field-magnets can be made of any wood, well finished, and , 
sent to the nearest foundry. These patterns should be | 
just a trifle larger than desired for the finished casting, as j, 
there is a shrinkage for which there must be an allowance, j^ 
Castings and machine work will cost but little. 



Chapter XXI 

CHANGING ELECTRICAL ENERGY INTO HEAT 

HEAT is but another form of energy. 
We know when anything is hot or cold, but few of 
us know how or why. Heat is so common that one hardly 
gives it a thought, yet it is equally as mysterious, as in- 
visible, and quite as puzzHng as electricity. 

In the old days heat was thought to be an elastic fluid 
called caloric, which permeated all substances. Now we 
know that heat is not a fluid, any more than electricity is 
a fluid. The assumption is that heat is the rapid to-and-fro 
vibration of the molecules of all matter which produces 
the result we recognize as heat. All this is mere theory, of 
course, but it is amply born out by research and experi- 
ment. This explanation of heat is known as the kinetic theory. 

Kinetic is taken from the Greek kineo, meaning to move. 

Heat is measured by a thermometer, or a "heat measure," 
as the word signifies. The ordinary Fahrenheit thermom- 
eter, such as is generally used, is marked zero 32° below 
the melting-point of ice. Scientists usually employ the 
Centigrade thermometer. In this the melting-point of ice 
is marked zero, and the boiling-point of water is at 100°. 

What We Know About Heat 

Heat is almost as wonderful as electricity. It seems to 
be very closely related to light and electricity. It is a very 

199 



HARPER'S BEGINNING ELECTRICITY 

possible experiment to focus sunlight through a lens made 
of ice and set fire to a bit of lint while the ice itself is not 
melted. A steel bar is longer when it is hot than when it 
is cold. In fact, heat expands most materials and cold con- 
tracts them. Iron bridges, steel rails, structural iron-work, 
etc., have to be designed to allow for this expansion and 
contracrion due to changes of temperature. 

According to the accepted theory, the molecules of all 
matter are at rest at a temperature of absolute zero. This 
is colder yet than hquid air, which is — 200° Centigrade. Ab- 
solute zero is supposed to be — 273° Centigrade. 

Scientists hold that all matter is made up of little mole- 
cules far smaller than the most minute object visible with 
the aid of a microscope. As soon as the temperature, is 
raised above absolute zero by the application of heat-energy, 
these molecules begin to move to and fro. The higher the 
temperature is raised the faster they move and the farther 
they swing. 

Whether things are soft or hard, rigid or flexible, brittle 
or resilient, depends upon temperature. The hardest steel 
armor-plate is as soft as rubber when red-hot and can be 
made to flow like water. Quicksilver is a liquid metal at 
ordinary temperatures, but it can be made hard enough to 
ring like the hardest steel by dipping it in liquid air and 
lowering its temperature. Apply a Httle heat, and it will 
disappear into vapor. 

Water easily freezes into ice. Lower the temperature 
of ordinary air sufficiently, and it becomes a liquid. Many 
gases can be made into liquids in this way. At absolute 
zero, it is believed, all gases would be solidified. 

Water and all other Hquids are due to temperature. 
The molecules vibrate just far enough to permit them to 
roll one over the other. Apply a little heat to move them 

200 



ELECTRICITY PRODUCES HEAT 

faster and they will fly out into the air and become gases. 
When you pour water from a pail the molecules roll over 
each other like peas. The molecules will leak out of any 
hole in the pail, or will roll out when the pail is tipped; but 
otherwise they cannot escape. Gases have to be confined 
on all sides because the flying molecules will escape from the 
tiniest hole. 

Apply heat to one end of an iron bar, and it will quickly 
travel to the other end of the bar. This is because the 
swinging molecules in the hot end of the bar beat against 
those adjacent to them and cause them to swing in har- 
mony. In this way the molecular motion is transmitted 
the length of the bar and the iron gets hot for its entire 
length. 

Relation Between Heat and Electricity 

Connect the iron bar to the poles of a powerful electric 
generator, and it will also become hot. Hotter and hotter 
will it grow until it is red-hot, then orange, then white, and 
finally it will sag down in the middle and break. If the bar 
is surrounded with a heat-resisting tube it can be made to 
boil like water, can even be vaporized into gases. 

This wonderful electric heat is caused by resistance. 
Electricity travels at the rate of 186,000 miles a second over 
a good conductor, such as copper wire. Place an obstruc- 
tion in its path and the energy of the flowing current can 
be changed into heat-energy. The current will work hard 
to overcome and get by this obstruction in its path. Work 
always produces heat. The greater the resistance, or the 
work required, the more heat produced. 

Electricity is the only form of energy which can be 
changed into heat without serious loss. When electricity 
J 13 201 



HARPER'S BEGINNING ELECTRICITY 

is purchased for cooking purposes none escapes up the 
chimney, and very Httle radiates out into the room. 



How Electric Heat Is Produced 

The secret of every electric heating or cooking device is i 
a carefully calculated bit of resistance wire or stamped | 
metal embedded between mica or porcelain insulators and | 
concealed within the device itself. German-silver wire is j 
commonly used for this work, although several new alloys . 
of various metals have been successfully developed. 

Sir Humphry Davy first reaUzed the enormous heat 
possible with electricity. With his first carbon arc, supplied 
with current from a two-thousand-cell battery, he dem- I 
onstrated that all known substances could be quickly 
melted and fused in the terrific heat of the arc. Diamonds, 
quartz, and rare metals were easily melted down, carbon 
boiled quickly away, even the fire-bricks of his crude oven 
were consumed. 

Heat from electricity is so terrific that temperatures of 
3,500° Centigrade are easily obtained. If scientists could 
only find something capable of holding higher degrees of 
heat there is hardly a limit to the temperatures that might 
be obtained. 

Electric welding, electric smelting of refractory ores, 
electric tempering-baths are now common enough in the 
industrial world. Wherever heat is required in manu- 
facturing electricity has been put to work. 

Measuring Heat 

I 
Years ago an English physicist, James Prescott Joule, 

made a complete study of the relationship between elec- 

202 




DIFFERENT TYPES OF ELECTRIC COOKING DEVICES 




PHANTOM VIEW OF ELECTRIC FLATIRON, SHOW- 
ING FLAT "leaf" heating -unit IN IRON 



ELECTRICITY PRODUCES HEAT 

tricity and heat. Joule proved that a certain amount of 
heat is produced in every conductor by the passage of an 
electric current. He ran a fine wire through a vessel con- 
taining alcohol in which he placed a thermometer. By 
sending a battery current through this wire and watching 
the thermometer he could measure the heat produced by 
any current. The current strength, the resistance of the 
wire, the heat capacity of the liquid, and the time being 
known and compared with the raise of temperature. Joule 
worked out his law. 

Dr. Joule determined by experiment that 778 foot-pounds 
of work would raise the temperature of one pound of wa- 
ter 1° Fahrenheit. This has since been adopted as the 
official unit for measuring heat. It is called the British 
thermal unit, and it is generally abbreviated by the let- 
ters b. t. u. 

No more mysterious source of heat can be imagined than 
that afforded by electricity. Without flame, smoke, or 
gases it is ready in an instant, and can be regulated at will 
from a slight warmth to the carbon-melting temperatures 
of the electric-arc furnace. The convenience, speed, and 
cleanliness of electric heat has led to many new develop- 
ments in electric household devices. 

In many cities where electric cooking has been common 
enough for years, it has been proven that electric heat is 
equally as economical as coal or gas, and especially so where 
cheap electricity is available from near-by water-powers. 
It is certainly more convenient, being available instantly at 
the touch of a finger, and vanishing just as quickly when its 
work is done. It is cleaner and more sanitary, doing away 
with the handhng of dirty fuels and ashes, eliminating 
poisonous gases and noxious fumes. 

20^ 



HARPER'S BEGINNING ELECTRICITY 



Explaining the Electric Iron 

The way electric heat is applied to household work is best t 
explained by using the electric iron as an example. The 
flexible cord of the flatiron, which is connected to the electric- 
lamp socket, contains two insulated wires. When the cur- 
rent is turned on, the electricity flows down one of these j^ 
wires at the rate of 186,000 miles a second. It passes '' 
through the resistance-leaf concealed in the bottom of the ' 
iron. In overcoming this resistance heat is produced, and 
soon the leaf becomes quite hot. This heat quickly radiates 
throughout the iron, keeping it at just the right tempera- ' 
ture for the work in hand. After the electricity has forced ' 
a passage through the resistance-leaf it has lost some of 
its energy, which has been changed into heat-energy, and 
flows up the second wire in the cord and back over the 
circuit. 

It seems almost incredible, yet it is true, that one can 
cook a dinner with the energy derived from faUing water. 
A portion of the water which plunges over Niagara Falls 
is diverted and guided through steel pipes to the revolving-? 
blades of giant turbine water-wheels. These water-wheels f 
are connected to powerful electric generators. The energy f 
of the falHng water is changed into mechanical energy by, 
the water-wheels, then into electrical energy by the dynamos. ^ 
This electrical energy is next directed to large transformers,! 
where the pressure, or voltage, is raised for transmitting itF 
to the distant towns and cities where it is used. In Syracuse, ' 
nearly two hundred miles away, the energy of Niagara is 
used to heat electric flatirons and other heating and cooking 
devices, as well as for light and power. 

The great advantage of electric heat is that it can be*^ 

206 



ELECTRICITY PRODUCES HEAT 

produced exactly at the point of use and the temperature 
is always under exact control in any degree desired. 

There are only a few experiments suitable for the labora- 
tory of the amateur to prove the existence of electric heat. 
It has already been noted that the spark from the static 
machine or the induction-coil is very hot. Such sparks 
will explode powder, ignite gasolene, and even scorch cloth 
or paper. If a very fine piece of iron wire the size of a hair 
be placed in circuit with a charged Leyden jar the wire 
will be easily melted. 

Advantage is taken of this fact in building the little pro- 
tective fuse for house circuits. Every house circuit is pro- 
tected from heavy currents, which might possibly surge 
over the line, by a little device called a fuse. The fuse is 
merely a bit of lead wire inside a small porcelain and brass 
plug with a mica covering. This plug is screwed in the fuse- 
box, located in the basement or the attic where the wires 
enter. The lead wire will permit only a small current to 
enter the house. If it is a ten-ampere fuse only ten amperes 
of electricity can be drawn over the wires at any one time. 
Any attempt to draw more current over the wires will heat 
up this bit of lead wire, over which the current must pass 
to get into the house, until it melts and thus breaks the cir- 
cuit. 

Experimenting with Electric Heat 

With the current from several batteries placed in series, 
or with the secondary current from the induction-coil, it is 
possible to study the heating effects of electricity. The 
best way to investigate this is to follow the excellent ex- 
ample set by Dr. Joule and submerge a piece of resistance 
wire in a glass jar of water in which is also placed a ther- 
mometer. 

207 



HARPER'S BEGINNING ELECTRICITY 

The rate at which heat is produced in am* wire through 
which is flowing an electric current can be accurately deter- 
mined. It is always directly proportional to the product 
of the resistance in ohms and the square of the current in 
amperes. 

Common iron wire, in the vet}' smallest sizes, is suitable 
for experimental electric heating. This wire offers con- 
siderable resistance to the passage of am- electric current. 
This resistance will cause the wire to get quite hot when 

a current of an}- strength 
is sent through it. Arrange 
the wire in a loose spiral 
and submerge it in a glass 
jar containing water. Meas- 
ure the temperature of the 
water with a thermometer, 
then allow the secondary 
current of the induction- 
coil to discharge through 
the resistance wire for one 
minute. Xow measure the 
temperature of the water 
again and note how much 
it has been raised b}- the pas- 
sage of the current Tig. i . 
It will be shown by these experiments that the heat pro- 
duced will depend upon the size and length of the wire 
used and the strength of the current passmg through it. 
An_v kind of a wire can be used. All will show that some 
heat is produced. Copper, brass, and aluminum being 
better conductors of electricit}- than iron, nickel, and lead, 
the}" will not produce as much heat as the latter, even if the 
wire is the same size and length. 

208 




Fig, t 



ELECTRICITY PRODUCES HEAT 

Short lengths of these fine wires can be readily melted 
and even fused by the current from a Ley den jar or from 
the induction-coil. Lead wires melt very readily. If no 
lead wires are available the lead can be rolled or hammered 
very thin and cut into strips. 



Chapter XXII 

ELECTRICITY AND LIGHT 

THE first hint of the possibihties of producing hght by 
electricity was the static spark and the hghtning-flash. 

When Newton was experimenting with his first static 
machine he noticed a mellow glow on the glass, and fore- 
saw the electric light. For many years it was the dream of 
every scientist to perfect the new light. Sir Humphry 
Davy had the secret in hand when he produced the first 
arc-light with his powerful battery. But the electric light, 
like the motor, had to await the subsequent development of 
the dynamo. [ 

Light and heat seem to be very closely related. | 

Always w^hen heat reaches a certain degree of intensity \ 
it produces light. Electric light is dependent upon heat, jj 
Heat can be produced without light. Electric light cannot 
be produced without heat. 

The common firefly produces the most perfect light known. 
This light from the firefly is practically a "cold " light. There 5 
is very little heat in proportion to the light. Years of re- i 
search have failed to read this riddle of nature. No one ' 
knows how the firefly can produce this light. It is thought ' 
to be very closely related to electricity. i 

Light travels at nearly the same speed as electricity, j: 
186,000 miles a second. The source of all light, except that |: 
of the glow-worm and the firefly, is a substance raised to such h 

210 



ELECTRICITY AND LIGHT 

a high temperature that it sets up Hght-waves in the sur- 
rounding ether. This wave-motion cannot be seen. The 
color of Hght depends upon the length of the waves. The 
light-waves producing blue light are very short compared 
with those producing red light. A red lamp gives off only 
red wave-lengths, which, faUing upon the eye, produce the 
sensation of red. 

Color Depends upon Light Rays 

In the dark there is no color. You can prove this by 
trying to illuminate a red cloth with a blue light. Since 
the red can only reflect the long waves, and the blue light 
gives only short waves, there is no reflection to the eye, and 
the cloth appears black. Black absorbs light. White re- 
flects it. A body appears white when it is reflecting all the 
light rays. If it absorbs all but the red rays the body will 
appear red. 

It is estimated that every square inch of the sun's sur- 
face gives off" 600,000 candle-power of light. The arc-lamp 
ranks next, with 10,000 candle-power per square inch. The 
new metal-filament incandescent lamps give 1,000 candle- 
power per square inch of filament. 

Absorption is the great natural enemy of light. Dark 
surfaces of all kinds absorb light. White surfaces reflect it. 
Therefore, it is easier to light a room finished in white than 
it is one finished in dark-brown, dark-red, or green. 

First Electric Lighting 

The very first application of electricity for lighting pur- 
poses was in street-lighting. It is difl[icult for us to imagine 
that the streets of our largest cities were almost totally dark 
less than a hundred years ago. With almost every city 

211 



HARPER'S BEGINNING ELECTRICITY 

boasting of its 'Svhite way" it is hard to picture New York, 
Boston, Philadelphia, Albany, Baltimore, Charleston, and 
other cities plunged in almost total darkness soon after the 
sun went down, as was the case less than a hundred years 
ago. The stores closed with the sun, and shop windows 
were never illuminated. Shutters were drawn tight. Some- 
times the better class of taverns maintained big glass and 
tin lanterns, burning a tallow candle, which lighted a tiny 
space of street about the entrance of these ancient inns. 
Men and women carried lighted lanterns whenever they 
ventured forth at night. 

It is true that Broadway, New York, now world-famous 
as the Great White Way, was even more notorious in the 
eighteenth century as the scene of nightly robberies, mur- 
ders, and other nefarious work of ruffians. Broadway at I 
that time was darker than the proverbial stack of black 
cats, and it was absolutely unsafe for any one to travel 
on the street after dark unless accompanied by an armed 
guard and lights. To-day it is a veritable fairyland by 
night, with mile after mile of brilliant electric lights, dazzling 
in every color of the rainbow, and resplendent in all the 
glory of artificial illumination. 

In only a very few of the larger cities of the United States 
was any attempt made to light the streets prior to the Revo- | 
lution. In Philadelphia, New York, and Boston a few street- 
lamps were maintained at pubhc expense on the principal 
thoroughfares. These lamps burned vegetable or sperm oil. 
They gave but a very feeble light, and required consider- 
able attention. 

Soon after 1783 the common councils of the various 
American cities voted to have the main streets lighted. ^ 
Open-flame oil-lamps were used, burning for the most part 
sperm oil. At best they gave a flickering light which served 

212 





ORNAMENTAL LUMINOUS ARC-LAMP 
FOR STREET ILLUMINATION 



MECHANISM FOR ORNAMENTAL 
LUMINOUS ARC-LAMP 




DIRECT-CURRENT, MULTIPLE, INCLOSED 
FLAME ARC-LAMP FOR INDOOR USE, SUCH 
AS FACTORY AND STORE ILLUMINATION 



MECHANISM OF MULTIPLE, INCLOSED 
FLAME ARC-LAMP 



ELECTRICITY AND LIGHT 

more as a beacon to pilot one along through the darkness 
than as an actual source of illumination. Lanterns were 
still carried, and every coach was equipped with side-lamps. 

Sperm oil was too scarce to be an economical source of 
Hght for streets, and very little progress was made in street- 
lighting until the great oil -fields of Pennsylvania were 
opened. In the early fifties the new mineral oil began to 
be used very extensively, and in a few years every city was 
dimly lighted with oil lamps. A number of small villages 
throughout the country still use these oil-lamps to light the 
streets. 

But oil-lamps gave way before the open-flame gas-light, 
and for a number of years gas companies were organized all 
over the country, and the streets of the larger cities were 
lighted with gas-flame lamps. 

But another and a better light was even then being com- 
pleted. Way back in 1809, when the world was still groping 
in darkness, Sir Humphry Davy, of London, was experi- 
menting with the electric arc. But the first electric street 
Hght was not perfected until 1881. Since then the develop- 
ment of the arc-lamp has been steady, until the finished 
product to-day gives the nearest possible approach to sun- 
light in artificial lighting. 

The electrical arc-hght was in actual service before the 
incandescent lamp was discovered. It was apparent to 
every one who saw those first arc-lamps that electricity was 
far ahead of any other illuminant for street-lighting. 

The Arc-Lamp 

An ordinary street arc-lamp is merely an adaptation of 
Davy's discovery. A current of about 500 volts is used. 
Within the lamp are two sticks of carbon placed end to end. 

215 



HARPER'S BEGINNING ELECTRICITY 

\A hen the current is turned on it readily passes through 
both pieces of carbon. At this instant a tiny electromagnet 
pulls the upper carbon away from the lower, forming a slight 
air-gap over which the current arcs. This arc produces an 
intense heat. The tips of both carbons become white-hot, 
throwing out a flood of light. Soon a crater of boihng car- 
bon will be formed in the upper carbon. It is this seething j 
crater which produces most of the light. After a little these 
carbons burn awa}'. As soon as they burn so far that the 
current cannot arc across, the lamp goes out. Instantly the 
little electromagnet loosens its hold and the upper carbon 
drops down of its o^vn weight, making a new connection. 
As soon as the current flows the magnet renews the arc, and 
the light is scarceh' interrupted. This explains the '"click" 
and "flicker" of the arc-lamp. This ''feeding" of the car- 
bon is accomplished so quickh* that it is scarcely noticeable. 
\\ hen the carbons have burned away ther must be replaced. 
The arc-lamp has been greatly improved upon of late 
years by the luminous and flaming arc-lamps, which give 
many times more light for less current. In the luminous 
and flaming arc-lamps the carbon rods are impregnated 
with various minerals which are easily made luminous by 
the application of heat. When these mineral particles, in 
the form of vapor, are heated to incandescence by the arc 
they add wonderfully to the amount of light. They also 
change the color of the light. Some of the lummous arcs 
give a white light, others are yellow or orange. 

Making a Miniature Arc -Lamp 

A miniature arc-lamp can be made with two ordinary [ 

lead-pencils. The "lead" in a pencil is really carbon. By ;, 
sharpening two pencils and notching each near the top so 

216 



ELECTRICITY AND LIGHT 

the carbon is exposed, a tiny arc-lamp effect can be secured. 
Connect the terminals of a hand-generator or several battery 
cells to the pencils and note the arc effect when the pencil- 
points are touched and then separated a hair's - breadth 
(Fig. I). 

If this experiment is tried on the house-voltage, care 
must be taken not to short-circuit the line. Resistance 
must be inserted between one of the pencils and the line. 
A "bank" of three ordinary i6-candle-power incandescent 
lamps will be sufficient. One pencil is placed in series with 



— =^^^M 




the lamps. This will permit only a small amount of cur- 
rent to flow through the pencils. When the pencils are 
connected to the wires of a flexible cord, and carefully taped, 
turn on the current. Taking care not to touch the exposed 
carbon, hold a pencil in each hand and bring the points 
together. Immediately the incandescent lamps will be 
lighted. Now separate the pencil-points slowly, and a bril- 
liant arc will be formed. If you pull the pencils too far 
apart the arc will be broken. 
When you have tried this experiment you will marvel at 

217 



HARPER'S BEGINNING ELECTRICITY 

the delicate mechanism of the street arc-lamp, which always 
keeps the carbon pencils at just the right distance apart, 
no matter how fast they burn away. 

The Incandescent Lamp 



Incandescent lamps differ very materially from arc-j 
lamps. The arc-lamp is burned in the open air. The in 
candescent lamp would be but a flash if air was admitted to 
the globe. The incandescent electric lamp is but a tiny 
thread of high - resistance material inclosed in a vacuum 
globe. 

The incandescent lamp really gives very little light in 
proportion to the amount of energy consumed. More than 
ninety-five per cent, of the electrical energy in an incan- 
descent lamp is wasted in heat. This heat merely radiates 
away into the surrounding air. In the light of the firefly 
these conditions are reversed, and the greater part of the 
energy is turned into light. Only a very little heat results. 
The "cold" light is the dream of most scientists. 

The light from a common incandescent bulb seems to 
be instantaneous. In reality a great many things happen 
in the lamp before the light comes on. When the switch is 
turned it closes the circuit so the current can flow to the 
lamp. The electric current rushes along the copper wires 
at the terrific speed of 186,000 miles a second. If the wires 
were not insulated at every point this energy would jump 
off and refuse to do its w^ork. When the electricity reaches 
the lamp it readily flows through a bit of platinum wire to 
reach the filament. Here it reaches its first serious resist- 
ance. In its path are several loops of a fine wire which 
is not a good conductor. But the electricity cannot turn 
back. With all the pressure behind it it must go on. It 

218 



\ 




EARLY TYPES OF INCANDESCENT LAMPS 
USED ABOUT 1880 




NEW METAL-FILAMENT INCANDESCENT LAMP. 

THE FILAMENT FOR THIS LAMP IS DRAWN 

FROM THE RARE METAL TUNGSTEN 



ELECTRICITY AND LIGHT 

pushes and forces a way over the obstruction, and this 
requires a tremendous amount of energy. This work con- 
sumes the electrical energy, just as it would consume me- 
chanical energy or human energy, and the energy thus 
consumed is not really destroyed — for nature never totally 
destroys anything, but it is changed into heat. As the 
current forces its way through the fine wire the electrical 
energy is rapidly changed into heat, and this heat quickly 
brings the wire to a white glow, when it is a fairly good 
conductor. 

The wire first gets warm, then hot, then a dull cherry- 
red; and finally this red fades, as it gets hotter, to a white- 
hot glow which is maintained as long as the current is 
turned on. The heat resultant from this process is rapidly 
dissipated into the air. 

Metal-Filament Lamps 

Incandescent-lamp filaments are now made of the rare 
metal tungsten. This metal is purified in the electric fur- 
nace and then drawn into wire finer than a hair. Tungsten, 
or Wolfram, is a metal discovered in 1781 and named from 
the Swedish "tung" (heavy) and "sten" (stone). 

The pure metal, which was produced only a few months 
ago in the electric furnace, is a bright steel-gray in color. 
It is also used to increase the temper and tenacity of steel 
for hard tools. The fusing-point of tungsten is higher than 
almost any other metal, which enables it to operate at the 
very high efficiency obtained in the tungsten lamp. 

Tungsten lamps are made on the same principle as the 
common incandescent lamps. They look about the same, 
but the filament is longer, looped several times in the glass 
bulb, and anchored at both ends. 

221 



HARPER'S BEGINNING ELECTRICITY 

It is not alone because the tungsten lamps give a better 
quality of light than any other artificial illuminant that they ' 
take first place in the hghting world. But this new lamp 
is the perfection of economy, and will give three times as 
much light as the ordinary electric light for the same amount ; 
of current. The ordinary incandescent lamp consumes 3.8 
watts of electricity per candle-power. The new tungsten 
lamp consumes only 1.2 watts, or less than a third. This i 
means that with the same amount of illumination the electric- [ 
light bills are reduced two-thirds. The life of these lamps j 
is about 1,000 hours, and they work equally as well on direct 
as alternating current. 

The Vapor-Lamp M. 

There is still another form of electric light called the 
vapor-lamp. The best type of this is the mercury-vapor 
lamp, which is a large glass tube, somewhat similar to the 
Geissler tube, containing a small quantity of mercury. The 
air is partially exhausted from the tube. A platinum wire at j 
each end carries the current to the lamp. When the lamp is 
tilted so the mercury flows from one terminal to the other 
it establishes a long arc of briUiant greenish flame. This 
glow will continue as long as the current is turned on. 
These vapor-lamps are very economical, producing light at 
a very low cost. But, unfortunately, the light lacks red 
rays, and is always of a greenish cast, making it of little 
use except for factory and street lighting. 

Experiments with electric lighting must be confined toj 
static sparks and Geissler tubes. 

It is hardly possible for any one to make incandescent 
lamps without a suitable air-pump to exhaust the globes. 
If the tiny filament of an incandescent lamp were placed in 

222 







MECHANISM OF HOUSEHOLD OZONATOR, SHOWING VIBRA- 
TOR, TRgANSFORMER, AND SPARK -TUBES. THE DEVICE 
PRODUCES OZONE GAS (a POWERFUL DISINFECTANT) BY 
DISCHARGING HIGH - POTENTIAL CURRENT ACROSS AN 
AIR-GAP 




EIGHT -INCH ELECTRIC FAN. THE FAN IS REALLY A 

PROPELLER FAN MOUNTED ON THE SAME SHAFT WITH 

THE ARMATURE OF THE TINY MOTOR 



ELECTRICITY AND LIGHT 

a circuit surrounded by air it would burn up in a flash. 
With the air exhausted it cannot burn. 

Miniature incandescent lamps can be purchased in all 
sizes, and at any voltage, for experiment work. It is hard- 
ly possible to make these lamps, even in the best of amateur 
workshops. They can be purchased for a few cents each. 
These tiny lamps are rated for 2, 4, 6, 8, 10, and 12 volt 
currents, from one to eight and ten candle-power. 

Never try to burn a 2-volt lamp on a 12-volt circuit. 
The lamp will burn up in a few seconds. If a 12-volt lamp 



t 



t 



12 VOLT 



1 



i 



SIX 2-VOLT LAMPS 
ACROSS 12-VOLT LINE 



VV^^ 



MtNIATURE LAMPS 
IN MULTIPLE 



MINIATURE LAMPS IN SERIES 

is placed on a 2-volt circuit it will give no light, because 
there is not voltage enough to heat the filament to in- 
candescence. 

There are several ways of connecting up these miniature 
lamps. They can be connected either in multiple or in 
series. If it is desirable to use 2-volt lamps on a 12-volt 
circuit use six of the lamps in series-multiple (Fig. 2). 
14 225 



HARPER'S BEGINNING ELECTRICITY 

Such miniature lamps consume a little over one watt of; 
energy for every candle-power. 

A candle-power, as the word suggests, is the amount of 
light given by a standard-size candle. Therefore a sixteen- 
candle-power lamp gives as much light as sixteen ordinary; 
candles. 



[ 



I; 



li 



Chapter XXIII 

WHAT THE BEGINNER SHOULD KNOW ABOUT THE ELEC- 
TRICAL EQUIPMENT OF AN AUTOMOBILE 

WITHOUT any attempt to play upon words, electricity 
is the vital spark of the gasolene-engine. 

Engineers speak of the gasolene-motor as an "internal- 
combustion engine/* Combustion is the action or operation 
of burning. A simple explanation of the engineering term 
is to say that an internal-combustion engine is one in which 
power is derived from the burning of explosive gases within 
the engine cylinder. Once this "charge" of explosive gas 
is compressed within the top of the cylinder ways and 
means must be found to ignite it. This ignition is best 
accomplished by an electric spark. In this type of engine 
the "charge" is usually gasolene mixed with air, forming a 
highly explosive vapor. When this is compressed and ex- 
ploded it imparts energy to the piston. The piston turns 
the crank-shaft. By a system of gears, shafts, or belts this 
energy is transmitted to the rear wheels of the vehicle. 

The gasolene "charge" is fired by electricity passing 
through the spark-plug. As the name suggests, the spark- 
plug is a small device screwed firmly into the cylinder top, 
which produces an electric spark hot enough to fire the 
vapor. This spark is merely the result of a high-potential 
current jumping across a small air-gap. Spark-plugs may 
differ in design and construction, but they all accomplish 
the same purpose. Insulated wires are brought down 

227 



HARPER'S BEGINNING ELECTRICITY 

through the plug to terminate in an air-gap. The com-, 
pressed gases surround these terminal wires, and at the, 
proper moment, when the piston has fully compressed the 
vapor, a hot spark jumps across this terminal and fires the 
charge. This spark is "timed" so it always comes at just 
the exact instant of high compression. Of course, there is 
a proper "time" for each cylinder, as the explosions must 
follow each other in the different cylinders in regular se-j 
quence. When the sliding piston is driven down by the 
expanding gas it opens a "port" near the bottom of the 
cylinder, where the gases escape into the exhaust-pipe and 
muffler. When the piston ascends, this "port" is closed 
and another opened to admit a fresh charge of gasolene 
vapor. 

Current-Supply for Ignition System 

The ignition system in an automobile consists of a source 
of current. This may be either a battery or a dynamo, 
or both. The supply is always direct current from a bat- 
tery, whether primary or storage, and of low voltage. If 
the dynamo is used to charge the storage batter}^ it is 
also direct current and low voltage. To raise this direct 
current to a potential sufficient to jump across an air-gap a 
vibrator and induction-coil are necessary. This vibrator 
and induction-coil are very similar to those of an ordinar}' 
induction-coil, and operate exactly the same way. The 
battery current of low voltage is interrupted by the vibrator 
and sent through the primary coil in rapid pulsations. 
This induces a current of high potential in the secondary, 
windings, which is carried to the spark-plugs over insulated 
wires. Fig. i illustrates the wiring plan for an ignition 
system in gasolene automobiles, showing the location of' 
battery, dynamo, switches, coil, etc. 

228 



i AUTOMOBILE ELECTRICAL EQUIPMENT 




Fig.t 

Of course, there are many systems of electric ignition for 
gasolene-engines. These systems are all alike in the main, 
however widely they may differ in design, as shown in 
Fig. 2. 

Electric Lights for the Automobile 

It has become the general practice to provide the auto- 
mobile with electric lights. Inasmuch as the machine must 
carry an electric system for ignition purposes, it is easy 
enough to enlarge the apparatus sufficiently to provide the 
car with lamps. Electricity has many advantages over all 
kinds of flame-lamps for automobile-Hghting. It is con- 
venient, efficient, clean, and always safe. Open flame and 
I lighted matches are always dangerous around a gasolene 
I car, and especially so in garages. From a switch on the 
I dashboard, within easy reach of the driver, the headhghts 
I 229 



HARPER'S BEGINNING ELECTRICITY 

can be thrown on for road-lighting. When running on towni 
or city thoroughfares the side-lamps can be switched on.p 
The tail-lamp can be lighted without walking around the' 
car. A tiny lamp can be used to illuminate the speedometer"! 
and other instruments, to light the steps or the interior oft 
the car. Another electric lamp can be easily arranged oni 
a long, flexible cord for trouble-hunting at night. Lighting!' 



PRIMARY 




Fig. 2 

' 230 



AUTOMOBILE ELECTRICAL EQUIPMENT 

matches within the interior of a car to locate repairs has 
destroyed a great many cars. 

It is vastly easier to push a button while the car is run- 
ning and light any of the lamps as desired than it is to stop 
and walk around in the mud to hght the oil and gas lamps. 
Electric lamps can be nicely adjusted to make the most of 
light reflection, owing to the absence of flame, soot, and 
intense heat. 

Automobile lamps are standardized at six volts. The 
touring-car of town or country will require the following 
equipment: 

Headlights: two 9, 12, 15, 18, 21, or 24 candle-power. 

Side-lights: two 3, 4, 6, or 8 candle-power. 

Rear light: one i}i, 2, or 3 candle-power. 

A lOO-ampere-hour storage battery weighing 55^ pounds 
will supply these lamps continuously for ten hours without re- 
charging. The battery will carry not only the lighting but 
also the ignition system. It replaces the gas-tank weighing 
probably 30 pounds, and the ignition battery weighing 
25 pounds, so that no additional weight is added to the car 
by the adoption of electric lighting. 

Automobile lamps have an efficiency of one watt per 
candle. It is easy to calculate the required equipment for 
any automobile. Two 21-candle-power headlights; two 
3-candle-power side-Hghts; one 2-candle-power rear light, 
operated by a six-volt battery, will require 50 watts of 
energy at a current of 8/^ amperes. A loo-ampere-hour 
battery will supply all of these lamps continuously for ten 
hours without recharging. As all the lamps are seldom 
used at the same time, the battery charge will really last 
much longer. Fig. 3, which is the wiring plan for auto- 
mobile-lighting, shows location of battery, switch, and 
lamps. 

231 



HARPER'S BEGINNING ELECTRICITY 



HEAD 




REAR 



Fig. 3 



The lamps should be so connected that either the side,' 
rear, or head lights may be used as desired, or all five lamps 
at once. 

Wiring the Car ' 

The wiring must be concealed as much as possible. It! 
must be amply insulated at all points. It should be "ar- 
mored" to prevent the insulation from wearing away. This| 

232 



AUTOMOBILE ELECTRICAL EQUIPMENT 



wire must be heavy enough to carry the low-voltage current 
without appreciable drop in potential, and should be con- 
nected to the battery through a suitable fuse. Low-voltage 
automobile lamps are very sensitive to a drop of voltage, 
which would be entirely permissible in a high-voltage cir- 
cuit. The wires between battery, or generator, and the 
dash-switch should be not less than No. lo. No. 14 wire 
should be used between the switch and the headlight, where 




Battery 
Rear 



L=^ 



Fig. 4 

the greatest current is used. The wires between the switch 
and side and rear lamps may be smaller, but it is good 
practice to use No. 14 wire for these. The switch must be 

233 



HARPER'S BEGINNING ELECTRICITY 



//eais^ 



S/^e 



%fh 



m 



i 



srw 









MK 



W 



/^^<r/^i^^/t2^/7 



n=^ 



//^r/? 






'f/cfe 



IT 



mim^ 







\^ 






/?e^/^ 



Fig. 5 



adapted for at least three separate circuits. It should be 
located within easy reach of the driver. Additional circuits 
may be installed, controlled by separate switches (Fig. 4). 

A good 15-candle-power electric lamp, with suitable re- 
flector, will project a beam of light 1,000 feet along the road 
and give enough light so that a newspaper can be read. 
Fig. 5 is a diagram showing the connection of automobile 
lamps to suitable push-button switches. 

The ordinary ignition magneto of most cars is usually 
large enough to supply current for both ignition and lamp 
service without a storage battery. Dry batteries in series are 
used to hght the lamps when the car is not running. It is 
not advisable to use the dry batteries any more than abso- 
lutely necessary. 

234 



AUTOMOBILE ELECTRICAL EQUIPMENT 



APPROXIMATE COST OF OPERATION OF AUTOMOBILE LAMPS, INCLUD- 
ING COST OF LAMPS AND ENERGY 

















Cost of 


Cost of 




NOMINAL 










Lamps and 


Lamps and 




CANDLE-POWER 






Hours 


Hours 


Current 


Current 


Number 






Total 


Amps. 


Burning 


Burning 


Per Hr. 


Per Hr. 


of 
Lamps 






Watts 


at 6 
Volts 






at 50c. 
Per Charge 


at 50c. 
Per Charge 






Amp.-Hr. 


on 100- 
Amp.-Hr. 




Per Lamp 


Total 






Battery 


Battery 


120 Amp.- 
Hrs. 


100 Amp.- 
Hrs. 


2 headlights 


24 


48 


48 


8 


15 


12 


$0,035 


$0 . 044 


2 headlights 


i8 


36 


36 


6 


20 


16 


.027 


.033 


2 headlights 


i8 
















2 side-lights 


4 
















I rear light 


2 


46 


48.5 


8.1 


14 


12 


.041 


.047 


2 headlights 


21 
















2 side-lights 


4 
















I rear light 


2 


52 


54-5 


9-1 


13 


II 


.044 


.051 


2 side-lights 


4 
















I rear light 


2 


10 


12.5 


2. 1 


57 


47 


.012 


.014 


2 headlights 


i8 
















(half time) 


















2 side-lights 


4 
















I rear light 


2 


46 


48. 5 


8.1 


23 


19 


.026 


.031 


(all time) 



















Cranking the Engine with Motor-Power 



Electric self-starters are being installed on nearly all the 
new-model cars. This equipment consists of a small but 
powerful current-generator, operated by the engine, a stor- 
age battery to supply current when the engine is not run- 
ning, and a suitable motor to "turn over'' the engine when 
starting. Sometimes this generator is also used as the 
starting-motor. A generator can always be used as a motor, 
or vice versa. When running, the generator charges the 
battery. When starting, the battery current is sent through 
the generator, which instantly becomes a motor, and 
*' cranks" the car. 

Where electric, starting-motors are used the wiring for 
the ignition and hghting systems remains the same as de- 
scribed. 

The generator is geared or belted to the engine-shaft. 
The process of charging the storage battery can be made 

23 s 



HARPER'S BEGINNING ELECTRICITY 

automatic. When the current drops to a certain level the 
battery draws current from the generator. When it is 
fully "charged" an automatic cut-out stops the flow of cur- 
rent until it is again wanted. In other cars the battery is 
fitted with suitable instruments for measuring the charge 
in the battery. A combined ammeter and voltmeter are 
usually employed. 

The Storage Battery 

Storage batteries, or accumulators, depend upon second- 
ary chemical action for their operation. They consist of 
certain materials so arranged that when a current of elec- 
tricity is passed through them they undergo certain chemical 
changes due to the current, and, if afterward connected to 
a closed circuit, will discharge a current nearly equal to the 
original charge. 

The material from which automobile storage-battery 
plates are made depends largely upon the use to which they 
are to be adapted. Batteries are now being manufactured 
with plates made of iron and nickel, lead and zinc, and lead 
and lead. 

In batteries of the lead-and-lead class the negative plates 
are made of sponge lead, which has a light-gray color and is 
very soft. The positive plates are of peroxide of lead, being \ 
dull chocolate in color and hard in texture. 

The electrolyte, or chemical, almost universally adopted 
for storage batteries is dilute sulphuric acid, made from pure 
sulphur. When fully charged the plates are pure lead for 
the negative and peroxide of lead for the positive. These 
have formed upon their surfaces during their normal dis- 
charge a very slight coating of lead sulphate. Upon re- 
charging, the sulphate upon the plates combines with the 
acid and dissociated gases, with the result that the positive 

236 



AUTOMOBILE ELECTRICAL EQUIPMENT 

plate again becomes peroxide of lead, arid the negative plate 
pure sponge lead. 

Thus it is seen that when the battery is being charged 
the chemical formation of the cells is changed. When the 
circuit is opened and the power turned on the chemicals 
work to regain their former state, and this work produces 
nearly as much electricity as it took to perform the change. 



Summary 

After all, this is but the beginning of electricity. With 
this knowledge properly mastered and assimilated the way 
on should be fairly easy. The most of us must be content 
with a fair "working knowledge" and a good understanding 
of electricity. A few will desire to take up the electrical 
profession as a business. For those who desire a more ad- 
vanced and complete knowledge of electricity there are 
books aplenty. Nearly all the large colleges maintain a 
course in electrical engineering. 

Scientists and men prominent in the great electrical in- 
dustry insist that electricity is still in its infancy. They 
predict that still more wonderful inventions and develop- 
ments are to come. The rivers and mountain streams are 
rapidly being harnessed to huge water-wheels, that their 
wasted energy might be saved for mankind. Every day 
electricity is finding new tasks to do. Everything, seeming- 
ly, that requires energy is being electrified. What the future 
holds no man knows, but certain it is electricity will take 
a prominent part in the future development of the great 
industrial world. 



^ 



^ 



Appendix 

A LITTLE HISTORY OF ELECTRICITY 

ELECTRICITY has ever been associated with mystery. 
The very word awakens an inborn fear of flashing Hght- 
ning and rolHng thunder. 

It is only recently that man has dared to tame and bridle this 
wonderful unseen and unknowable energy. It was only yester- 
day that we began to understand its nature — to realize its won- 
derful possibilities. 

To those few who have studied electricity it is no longer mys- 
terious. To those who daily utiKze it as a source of light, heat, 
and power it is no longer to be dreaded. Our forefathers feared 
the steam-boiler. They were afraid to ride on the first steamboats 
and in the first railroad-trains. But time has changed all this. 
Common knowledge and daily association with these things have 
removed the element of fear. In time electricity will also be too 
commonplace to be associated with fear or mystery. 

To fully understand electricity it is quite necessary briefly tc 
review the main steps of its evolution and development from the 
earliest known records down to the present time. Traced from 
Its humble beginning, the electric dynamo, or generator, becomes 
as simple and easy to understand as the steam-engine. The 

i electric motor is no more difficult to master than the sewing- 

j machine, once its vital principles are explained. 

I Lightning was, undoubtedly, the first known manifestation of 
electricity. 

! But the ancients did not know the truth about lightning. 

jThey thought that lightning and its accompanying thunder were 

1 evidence that the gods were angry. And they hurried to pacify 

jthis wrath by off^ering prayers and sacrifices. 

239 



HARPER'S BEGINNING ELECTRICITY 

The Greek god of the heavens, the mighty Zeus, was frequently 
carved in ancient marble with a thunderbolt grasped in his right 
hand. These thunderbolts were said to have been forged by the 
giant Cyclops, in subterranean furnaces, out of gratitude for being 
released from Tartarus. The smoke and rumble of volcanoes 
were said to be evidence that the Cyclops were hammering out 
new thunderbolts. Electra, *'the bright one," the daughter of 
Atlas and Pleione, was one of the seven Pleiades. 

The Romans interpreted the thunder as the voice of Jupiter, 
the god of the upper air. It was Jupiter who hurled a thunder- 
bolt and struck the son of Phoebus from the chariot of the sun and 
thus saved the world from flame. All the early pagan civilization 
accounted for lightning and thunder in this same way. Even the 
American Indians told strange legends about the Thunder Bird i 
whose wings darkened the sky and whose fiery eyes scorched the ' 
earth. The streaming, scarlet banners of the northern aurora, : 
which is caused by an electrical disturbance of the polar air, was f 
also interpreted by the ancients as a message of evil from the * 
gods. Not so very many years ago it was thought that the | 
aurora horealis was a sure sign of approaching wars and reigns of f 
disaster and blood. f 

Though a trace of this old superstition still remains to make 
cowards of us all when the hissing lightning leaps to earth and the 
mighty thunder rolls, scientists have solved this riddle of the 
clouds. Jupiter and Zeus and the Thunder Bird are no more. 



The Discovery of the Magnet 

Long before the first scientific records were written in books 
it was noticed that certain bits of iron ore would attract other 
particles of iron. The superstitious people of the East bowed down, 
in awe before this mysterious force. They could not understand' 
it. Things they could not understand made them afraid. Thesel 
peculiar pieces of ore, which possessed the wonderful property of 
drawing, or "leading,'' small pieces of metal, were called "leading- 
stones." This was finally corrupted into lodestones. As the firstj 
specimens of lodestones to reach Europe came from the ancienti 
city of Magnesia, they were called magnets. This was one of the> 
first words in our electrical dictionary. 

240 



APPENDIX 

For a long time lodestones, or magnets, were objects of mystery 
and amusement. A use was finally found for the magnet in the 
mariner's compass. The Chinese are given credit for this useful 
instrument, although its birthplace is very uncertain. 

The compass is the very first electrical invention. It was in 
actual use for a long time before it was described in a letter by 
Alexander Nickham, an English monk, in the year 1180. The 
Chinese have many old legends about the discovery of the com- 
pass, and when their old manuscripts are all read we may know 
the truth about its discovery and application. 

But some one, way back in the misty past, discovered that a 
lodestone, when suspended by a silk cord, will always assume a 
position which may be said to point north and south. This dis- 
covery itself was of no use until it was noted that steel needles, 
when rubbed against the lodestone, absorbed, or partook of, the 
same magnetic powers. On that day the compass was born. 
The first compass consisted of a magnetized steel needle hung on 
a silk thread. This could not be used on shipboard when the water 
was rough, so they thrust the needle through the top of a cork and 
floated it in a basin of water. This water-compass was held by 
an assistant while the helmsman steered the ship. It is quite 
unnecessary to say that these crude compasses were used only 
when it was too dark to steer the ship by the stars. Finally the 
needle was balanced upon a pivot, and in this form it has been 
used ever since. 

Columbus, Cabot, and other early mariners noticed that the 
compass did not point to the true north. They also noticed that 
this deviation varied with different localities. A London ocuHst 
in 1 5 16 noted that the compass needle could not be perfectly 
balanced on the pivot. It dipped toward the earth. These may 
be said to be the first recorded observations of the new science 
of electricity. 

Electric Fish 

History does not say when the first Mediterranean fisherman 

hauled in a torpedo-fish, or electric ray, and received a terrific, 

invisible blow when he attempted to handle the fish. This must 

have happened to primitive man, although it was not until fairly 

15 241 



HARPER'S BEGINNING ELECTRICITY 

modern times that this ''shock" from the captured fish was known 

to be of electrical origin. j 

There are a great many varieties of electric fish, from the tor- i 

pedo of the Mediterranean to the electric eel of South America. ' 

These South American eels attain a length of nearly six feet, and f 
can give a discharge sufficient to stun a horse. There are also 
several varieties of electric fish in Africa and along the Florida 

coast. All of these fish can give a heavy discharge of electricity | 

at will. This power seems to be used only for defensive purposes, f 

In the old days these electric fish were used for the cure of vari- ^ 

ous diseases. To this very day scientists do not know just how < 

these fish produce their supply of electricity. '' 



First Static Experiments 

There is no definite knowledge of who was the first to notice 
that amber, when rubbed with silk, will attract bits of paper, 
threads, lint, etc. Amber comes from the north Baltic countries, 
and is nothing more or less than fossilized resin. It was used very 
extensively in the arts and for ornamental purposes by the early 
Greeks. They called it "electron" because of its beautiful golden 
appearance, somewhat resembling crystallized sunshine. 

The Greeks wrote with a sharp-pointed stylus on a wax pad. 
This stylus was often made of amber. And thus it came about 
that the Greek students, playing between lessons with amber 
styluses and a few bits of lint, gave us the root "electron" from 
which grew the word electricity. ,, 

The founder of Greek philosophy, Thales of Miletus, 600 b. c, 1 
was familiar with the fact that amber possessed the power of f 
attracting bits of paper. It is also probable that he knew of the 
lodestone, for they are both older than civiHzation. 

When the Greeks recorded this strange property of amber the 
Romans were quick to take note, and Pliny, the elder, investigated |j 
it in A. D. 70. He thought the stone was rubbed into life by his r 
fingers. With all his numerous experiments he arrived no nearer 
a solution of the mystery. While the Romans believed that the j" 
great Jupiter hurled his thunderbolts in just anger, they little knew jl 
that their amber ornaments held the very secret of the lightning. 
The great Caesar was awed and astounded by strange lights which 

242 



APPENDIX 

on certain nights played ghostlike about the spiked helmets and 
spear-points of the Roman legions. He did not know that it was 
caused by electricity. When this same mysterious fire glowed 
from the masts of the triremes, or war-galleys, in the Roman navy 
it was interpreted as a message from the gods in assurance of 
victory. 

Only a few thinkers and dreamers in the early dawn of civiliza- 
tion stopped to study the magnet and the magnetic properties of 
amber when excited by friction with a silk cloth. They thought 
the magnet had a soul. They even imagined that they had dis- 
covered the secret of life. They did discover, however, that a 
! magnetic influence surrounded the magnet for a considerable dis- 
I tance. They spoke of this as the ^'orb of virtue." They said 
i that the magnet gave out invisible "rays of force." The distance 
I in which a magnetic influence is noticeable is now known as the 
I field of force. The invisible rays between the poles of a magnet 
are now called the lines of force. 

Then came the Dark Ages, when chaos reigned, and it is for- 
tunate that electricity was not forgotten when the great Roman 
civilization passed away. 

The First Book about Electricity 

The real history of electricity began when several European 
students took up its study. Dr. Gilbert, an Englishman, wrote 
a book on magnetism in 1600, recording a large number of in- 
teresting experiments. Gilbert noted that a magnet could be 
broken up into small pieces and that each piece would be a perfect 
magnet. In this way he discovered that the earth is a huge mag- 
net. He was the first to use the words north pole and south pole 
in connection with magnets. Gilbert told little in his book that 
was not already known, but he showed what might be accom- 
plished by research work. He stimulated every scientist to experi- 
ment and learn by observation and study. From his time began 
i the work in electricity which has steadily progressed down to the 
i present day. 

! Gilbert called all substances which attract light bodies when 
I rubbed "electrics." Those that did not attract he called "an- 
I electrics." The word electricity was not used in its modern sensq 

243 



HARPER'S BEGINNING ELECTRICITY 

until Sir Thomas Browne wrote it in his book on medicine in 1646. 
Browne used the word as a noun, his predecessors used it as an 
adjective. 

In 1 65 1 Otto von Guericke, of Magdeburg, which is in Saxony, 
Prussia, invented the air-pump. He exhausted globes, tubes, jars, 
etc. He made two hollow plates which ordinarily fell apart in his 
hands, but which could not be pulled apart by horses when put 
together and the air exhausted from the inside. His next world-, 
astonishing invention was a machine for producing electricity. 
Rubbing amber and glass rods did not give enough electricity foF; 
elaborate experiments. Guericke mounted a large ball of sulphur: 
on an axle and turned it with a crank. B}^ whirling the ball and 
pressing its surface with the warm hand or a silk cloth electricity 
was produced by friction. This was the first electric machine. 
It was also the first time electricit}^ had ever been produced in any. 
noteworthy quantit}'. This machine greatly stimulated further, 
experiments. 

Early Types of Static Electric Machines 

Isaac Newton, who discovered the law of gravitation, also ex- 
perimented with electricity. He improved upon Guericke's ma-. 
chine by using a glass instead of a sulphur globe. It is recorded; 
that Francis Hawksbee, while experimenting with one of these r, 
machines, put some quicksilver in a glass tube and exhausted the 
air with one of Guericke's air-pumps. He was surprised to see^ 
this tube glow with hght whenever it was brought into contact- 
with the electric machine. This was the first gleam of our modem, 
electric lights. Improvements were made on the friction-machine |j 
by G. M. Bose, who added the conductor; by J. H. Winkler, of; 
Leipzig, who substituted a leather pad for the silk cloth. Andreas ' 
Gordon, a Scottish monk, used a glass cylinder in place of the^ 
globe. 

Stephen Gray was experimenting with conductors in 1728, and: 
announced to the scientific world that electricit}^ collected only| 
on the surface of materials. He conducted a number of experi- 
ments to prove this. Gra^^ was one of the first to discover that ^ 
electricity would flow through certain materials and not through; 
others. Those which carried, or conducted, electricity he called 

244 



APPENDIX 

conductors. Those which did not carry electricity he called non- 
conductors. 

Soon thereafter the glass-disk friction-machine was invented, 
which produced large, brilliant sparks and enabled further experi- 
ments with the mysterious force. Du Fay, a Frenchman, used 
one of these machines and sent a spark through a cord over a 
thousand feet long, which was thought to be a wonderful achieve- 
ment. It was soon discovered that there are two kinds of elec- 
tricity, or two phases of the electric current. One is produced by 
rubbing glass and the other by rubbing resin. The first was 
called vitreous electricity, and the latter resinous electricity. 

The two phases of electricity were called vitreous and resinous 
until Benjamin Franklin advanced the theory that one side of 
the electric machine accumulated a store of electricity which was 
taken from the other side. This vitreous side he called positive, 
and the resinous side negative. Franklin also used the plus sign 
(+) to signify positive electricity, and the minus sign ( — ) to signify 
negative electricity. They are still in use to-day. 

Accidental Discovery of the Leyden Jar 

Professor Muschenbroeck, of Leyden, in 1745, tried to store 
electricity and produced the "Leyden jar," named after the city 
where is was discovered. The electric machines of those days 
gave at best a very limited amount of electricity. With the in- 
vention of the Leyden jar, as improved by Sir William Watson 
and Dr. John Bevis, it could be stored up until a sufficient quantity 
had accumulated for the most extensive experiments. This was 
the first intimation of the mighty energy of electricity. Huge 
Leyden jars, and batteries of jars, were constructed. These, when 
fully charged, produced enormous sparks, and the shock from the 
discharge was sufficient to stun an ox. 

The speed of electricity was not suspected until Sir WiUiam 
Watson sent a charge from a Leyden jar over two miles of wire. 
This experiment was tried over and over again. Always the 
charge was felt at the terminal the instant it was started on its 
way. This proved that electricity travels at an enormous speed. 
It was then thought to be instantaneous, the same as light. 
Modern invention has produced an instrument capable of measur- 

24s 



HARPER'S BEGINNING ELECTRICITY 

ing this speed, which will circle the earth nearly eight times in a 
second. 

It was in 1749 that Benjamin Franklin began the study of elec- 
tricity. He wrote many noteworthy papers on the subject, in 
which he prophesied many of the modern electrical wonders. 
With his kite and string Franklin proved that the electricity of 
the friction-machine and the lightning from the clouds are the 
same. This had been suspected but not proven before. Franklin 
charged his Leyden jars from the clouds and performed the usual 
experiments with the electricity accumulated in this way. Frank- 
lin invented the lightning-rod. His experiments were repeated 
in Europe, and he was honored as being the greatest scientist of 
the day. 

The Discovery of Induced Currents 

A few years later — in 1753, to be exact — John Canton, an EngHsh- 
man, discovered that electricity could be generated without actual ^ 
contact, or friction. This process he called induction, meaning 
that the current was induced in one material by moving it "within 
the lines of force" of a charged body. This was a most important 
discovery. Glass-disk machines for the generation of electricity 
by induction were immediately produced, and they proved more 
powerful than the old friction type. 

A number of European scientists continued the study of fric-f; 
tional electricity. Henry Cavendish, like Franklin, wrote a great ) 
deal about the theory of electricity. Cavendish experimented 
with the resistance of various substances. He also studied the |) 
eflPects of electricity on liquids and gases, opening a new field of j] 
scientific research. Cavendish was one of the greatest scientists 
of the eighteenth century. His work in electricity was most J 
valuable, inasmuch as it anticipated many of the most important 
inventions to come. 

Ebenezer Kinnersley, of Philadelphia, was one of the first to 
experiment with the fusion of metals by the electric current. 
Johann Karl Wilcke, of Sweden, also contributed to the knowledge 
of the subject. In 1773 John Walsh proved to the scientific 
world that the shock of the torpedo, or ray, was an electric one. 

The famous French inventor, C. A. Coulomb, who died in 1806, : 
also contributed a great deal of valuable information resulting 

246 



APPENDIX 

from his tireless researches. He is famous as one of the first to 
measure and record electrical effects. 

Up to this time, it must be remembered, static electricity, pro- 
duced by friction-machines, was the only kind known. For this 
reason electrical experiment remained practically at a standstill 
until the discovery of the chemical battery which gave a steady 
flow of current. 

The Birth of the Battery 

An Italian named Aloisio Galvani, a professor of anatomy in 
the University of Bologna, experimented with a static electrical 
machine in the year 1790. He discovered that frog legs were 
made to twitch, as though with life, when touched with an elec- 
trically charged wire. There is a legend to the effect that Galvani 
discovered this fact quite by accident. The story goes that his 
wife was sick and her physician recommended frog legs for her 
diet. These frog saddles were lying on the table when an elec- 
trical spark jumped to one of the legs, and it began to twitch. 
This story is very doubtful. The probabilities are that Galvani 
already knew, as others knew before him, that frog legs are very 
sensitive to weak electrical currents, and that he was using them 
for experimental purposes. 

In the course of his experiments Galvani hung the frog legs on 
a copper hook with the toes touching a zinc plate. This also 
caused the legs to twitch as often as the toes touched the zinc, 
evidencing a continuous current of electricity. Galvani recorded 
these facts, but made no use of the discovery. He thought that 
he had accidentally hit upon the great secret of life. 

It remained for another Italian, Alessandro Volta, to show that 
Galvani had really created an electric battery. 

Volta Makes First Wet Battery 

It is recorded that Volta was born in Como, Italy, in 1745. 
He was appointed professor of physics in the Gymnasium of Como 
in 1774, ^^d ^^^ years later was given the chair of physics at 
Paris. In 1801 he was called to Paris to demonstrate his wonder- 
ful electrical experiments to the great Napoleon. In 1815 the 

247 



HARPER'S BEGINNING ELECTRICITY 

Emperor of Austria honored him with the appointment of director 
of philosophy at Padua. Volta died twelve years later. 

In memory of this great inventor the pressure of the electrical 
energy is expressed in volts, as steam pressure is expressed in 
pounds. This is a monument to the great scientist which will 
exist as long as the electrical industry. 

Volta made the first chemical battery about 1799, while ex- 
perimenting with various metals and testing out the electrical 
effects on frog legs and the electroscope. Satisfied that he was 
on the right track, he constructed a pile of alternate sheets of 
copper and zinc. These sheets he separated with a strip of cloth 
moistened with salt water. When this pile was completed, with 
the bottom copper sheet connected to the top zinc sheet, it pro- 
duced a steady flow of electricity. In honor of Galvani, who 
really discovered the principle upon which Volta acted, this form 
of battery is still called a galvanic battery. 

As soon as Volta announced his discovery in 1800 scientists 
dropped their experiments with frictional electricity to take up 
the study of the battery. It was noticed at once that, while the 
friction machines gave but a small quantity of electricity, under 
great pressure, the battery gave a large flow of current at low 
pressure. 

A war of words began at once, because the scientists could not 
agree as to what caused the electricity in the battery. Even to- 
day they are not all agreed, although it is undoubtedly the action 
of the chemicals on the battery plates. 

Volta was not satisfied with the Voltaic pile, and reformed it 
into a "crown of cups." This was further altered by placing the 
metal plates in a long trough, separating each pair into a small 
compartment, or cell. And the single battery unit is called a cell 
to this very day. 

Powerful batteries of as many as a thousand cells were made. 
The batteries gave no brilliant sparks, but produced a powerful, 
steady current. With these large batteries water was decomposed, 
metals and carbon melted. Chemistry was revolutionized in a 
day, and scientific work was extended into many unexplored fields. 

As a natural consequence the battery was further improved by 
others who followed after Volta. A great number of types of the 
galvanic battery were produced, all acting on the same principle. 
W. Cruikshank, Dr. WoUaston, Robert Hare, Sir Humphry 

248 



APPENDIX 

Davy, and others greatly improved the battery. The chemists of 
Europe and America advanced their research work into wider 
fields with the aid of the new device. 

But the relationship between static electricity, magnetism, and 
the current produced by the chemical battery was not yet estab- 
lished. Those things which seem so simple to us now were slow 
in coming. 

About this time Andre Marie Ampere, of Lyons, began his 
famous experiments and discoveries. He demonstrated the fact 
that two parallel wires conveying electrical currents attract 
each other when the currents flow in the same direction, and repel 
each other when the currents flow in opposite directions. He 
also discovered several other natural laws of electricity. In 1821 
he thought of an electrical telegraph with a separate wire for each 
letter of the alphabet. This, however, was too expensive and cum- 
bersome to be practical. 

Ampere died in 1836, honored and respected as a great scientist. 
The quantity of electricity flowing through a conductor is now ex- 
pressed in aviperes in his memory. 

The First Electric Arc 

The credit for the first electric light is due Sir Humphry 
Davy. In 1808 the Royal Institution of England provided him 
with a battery of two thousand cells to assist him in his research 
work and the discovering of new metals. While engaged in a 
chemical analysis he attached two pieces of charcoal to the ter- 
minals of the two-thousand-cell battery. When these bits of char- 
coal, or carbon, were brought together and then separated a little 
a briUiant arc of flame jumped across the gap and burned with a 
dazzling light. Davy called this the electric arc. The heat from 
this arc was hotter than anything ever known before. All metals, 
stones, gems, etc., were quickly consumed by it. Davy did not 
produce an arc-lamp because such a lamp was impractical so long 
as batteries had to be used to supply the current. But this same 
principle is employed in the arc-lamps of to-day. 

The process of coating one metal with a thin sheet of another, 
called electroplating, was discovered in 1805 by an Italian chemist 
named Brugnatelli. He found that if the battery was filled with 

249 



HARPER'S BEGINNING ELECTRICITY 

a gold solution the passage of an electric current deposited a film 
of gold on the silver plate of the battery. This process was of 
great importance to the gold and silver smiths, as it enabled 
them to produce articles of an inferior metal and coat them with 
silver and gold. 

Hans Christian Oersted, a Dane, began the study of electricity 
about 1800, and soon found the metal aluminum. This in itself 
was a great discovery, but his greatest find was that magnetism 
is produced by electricity. This was the secret which all had 
sought. In the year 18 19 Oersted conducted a series of experi- 
ments which proved beyond a doubt the relationship of electricity 
and magnetism. He proved the existence of the magnetic field 
about a wire carrying a current of electricity. 

Oersted was professor of natural philosophy at Copenhagen. 
He died in 1851, when the development of electricity was well 
under way. 

When the Electromagnet Was New 

A Frenchman, D. F. Arago, made some magnets by putting 
bars of steel inside of spiral coils through which he sent an electric 
current. But the honors for the discovery of the electromagnet 
seem to be divided between William Sturgeon, of England, and 
Joseph Henry, of America. Joseph Henry was a professor of 
mathematics in the Albany Academy in 1826. He was one of the 
first to make insulated wire by winding it with silk. Henry dis- 
covered that a bar of soft iron could be made into a powerful 
magnet by winding it with his insulated wire and sending a cur- 
rent through the wire. When the current was turned off the 
magnetism ceased. Henry made several very powerful magnets. 
One of these, made in 1834, easily raised 3,500 pounds of iron and 
held it suspended as long as the current was flowing through the 
wire. 

The discovery of the electric generator, or dynamo, is credited 
to Michael Faraday. Faraday was bom in 1791, and when a 
young man became assistant to Sir Humphry Davy. Faraday 
was an apt pupil, and he was the first to discover that the energy 
of an electric current could be used to impart continuous motion 
to a mechanical body. Faraday made the first electric motor, 
although the idea had suggested itself to Oersted, Davy, Wollas- 

250 







EARLY TYPE OF BI-POLAR DYNAMO 




MODERN DIRECT-CURRENT DYNAMO, OR GENERATOR 



APPENDIX 

ton, Schweigger, and others, before Faraday's success. This first 
motor was but a little toy, but it served its purpose well. This 
little motor, no more than a revolving wire in a glass tube, con- 
tained the fundamental principles of the electric motors of to-day. 
Peter Barlow, of England, improved upon this first motor. 
Others helped to perfect it until Thomas Davenport, a Vermont 
blacksmith, made the first electric motor adapted to commercial 
use. 

Ohm Works Out Laws of Electricity 

A German professor of mathematics. Dr. George S. Ohm, dis- 
covered in 1827 that all materials resist the flow of electricity to 
a certain degree. With the aid of mathematics he worked out 
another of the natural laws of electricity. Ohm gave the world 
the formula for figuring out the amount of current flowing through 
a circuit in a given time. The difficulty a current meets in flow- 
ing through a circuit is very properly called resistance. The unit 
of resistance is named the ohm in honor of its German discoverer. 

About this time Samuel F. B. Morse attended a lecture and saw 
one^of Henry's powerful magnets in operation. Soon after this 
lecture Morse began his experiments which terminated in the 
electric telegraph some years later. 



The First Successful Electric Motor 

The electric motor owes more to Thomas Davenport, a poor 
Vermont blacksmith, than to any other person, although a num- 
ber of toy motors had been made before his time. Davenport was 
the first to make a motor possible for practical use. Working 
and experimenting in dire poverty, he developed his motor despite 
the greatest handicaps and discouragements. At one time, it is 
said, he was too poor to buy silk to cover the wires for his motor, 
and had to sacrifice his wife's wedding-dress. 

In 1837 Davenport ran a toy railroad in Springfield, Massa- 
chusetts, with one of his motors. That same year he made a 
motor large enough to operate a printing-press. The first elec- 
trical journal in the world was printed on a press driven by one 
of Davenport's motors. 

253 



HARPER'S BEGINNING ELECTRICITY 

Soon after this a man named Jacobi, a Russian, propelled a 
small boat on a lake near St. Petersburg with the aid of an electric 
motor. 

Of course, all these early motors secured their electricity from 
galvanic batteries. This is the reason why Davenport's motors 
could not at that time be used economically and successfully. 
The motor was ahead of its time and had to await the development 
of the dynamo, which made cheap electricity possible in any quan- 
tities desired. 

Discovery of the Dynamo 

Faraday knew that magnetism could be produced with elec- 
tricity. He thought that this process might be reversed. In the 
course of time he worked out a device for producing electricity 
directly from magnets. This was the birthday of the electric 
generator, or dynamo. It made possible all the subsequent develop- 
ment of the electrical industry. 

After many failures Faraday noted that whenever a circuit was 
made or broken a slight current of electricity was produced. 
By experimenting with a coil of wire and a powerful magnet he 
was able to produce a slight current in the coil by passing it be- 
tween the poles of the magnet. When the coils of wire cut the 
invisible lines of force between the magnetic poles a current was 
induced in the wire. This was the solution of the baffling prob- 
lem. 

Acting on this principle, Faraday made the first electric dynamo, 
in the fall of 183 1. Like its predecessor, the Faraday motor, it 
was but a toy. He mounted a copper disk upright in a frame so 
that it could be revolved between the poles of a magnet. When 
the disk was rotated, cutting the lines of force, it produced elec- 
tricity by induction. 

From this humble beginning the development of the electric 
generator was easy. 

Morse Produces the Telegraph 

The world was astonished when Morse completed his first tele- i 
graph at the University of New York in 1835. His first pubhc 
test of the new telegraph was in 1837. A patent was taken out 

254 



I 



APPENDIX 

in 1840, but its inventor was hungry and penniless and disgusted 
when the United States finally took up the telegraph in 1843 and 
proved it a success in every way. Soon the telegraph wires were 
extending everywhere, connecting every city and all parts of the 
country. The continent was crossed in 1861, in spite of Indians 
and buffaloes. Morse was also one of the first to experiment with 
the submarine cable. He covered a wire with gutta-percha and 
laid it from New York City to Governor's Island. A few mes- 
sages were exchanged before a ship fouled the wire with her 
anchor and broke it. Morse had no more money to lay another 
cable. 

Electrotyping for the printing industry was but a modification 
of the electroplating process. J. Adams, an American, succeeded 
in making electrotypes from type in 1841, and this process has 
been in daily use almost continuously from that early date. 

During the ten years intervening between 1840 and 1850 many 
laws relating to electricity and its conduct were discovered. In- 
struments for measuring electrical effects were also perfected by 
H. von Helmholtz, Sir Charles Wheatstone, C. F. Gauss, F. E. 
Newmann, W. E. Weber, J. P. Joule, Lord Kelvin, and others. 

The first successful submarine cable was laid across the English 
Channel in 1851. Cyrus W. Field attempted to lay a cable across 
the Atlantic in 1857, but it broke in midocean. Another attempt 
in the following year was more successful, but again the cable 
parted after 732 messages had been sent. In 1865 another At- 
lantic cable was lost. It was recovered in 1866, and has been 
successful ever since. Cables now connect nearly all the impor- 
tant islands and continents throughout the world. 



Perfecting the Dynamo, or Generator 

The electric generator, or "magnetic-electric machine," as they 
were first called, which Faraday had invented, was improved from 
year to year. One of the first machines was made by H. Pixii in 
1832, who invented the split commutator for reversing the cur- 
rent through the armature. Other improvements were made by 
J. Saxton, E. M. Clarke, and others. In 1857 E. W. Siemens 
invented the shuttle type of armature and improved the field- 
magnets. The dynamo became a commercial success in 1866-67, 

255 



HARPER'S BEGINNING ELECTRICITY 

and was used for all purposes where large amounts of electricity 
were required. 

As far back as 1841 a large "magnetic-electric machine" was 
driven by a steam-engine. F. H. Holmes, in 1862, used permanent 
magnets and multiple poles for his dynamo which was used to 
supply current for a lighthouse. The generator, or dynamo, was 
also improved by Dr. Antonia Facinatti and Gramme in 1870. 
Three years later it was discovered, by accident, that a dynamo 
was also an electric motor. When the belt slipped off a dynamo, 
which was being driven by a steam-engine in company with several 
others, it continued to run, drawing current from the other 
dynamos in operation. All efforts to stop the runaway failed. 
In this way the enormous power of an electric motor was dis- 
covered. The toy motors previous to this had no more than hinted 
at the power possibilities of the electric motor. 



The First Arc-Lamps 

The development of electric lighting was also very slow. Sir 
Humphry Davy, as noted, produced a brilliant arc between two 
carbon electrodes. 

Two arc-lamps were installed in prominent public squares in 
Paris in 1844 by Deleuil and Archereau, two French inventors. 
The device showed possibilities, but the regulating mechanism 
was defective. The inventors wanted to perfect the lamps, but 
the cost for the battery current prohibited the success of arc- 
lighting at that time. 

The first successful arc-lamps were used in lighthouses in 
England and France. 

But it was not until 1876 that a Russian officer produced 
the "electric candle." This arc-lamp was a commercial success 
and was used in a number of European cities. Two years later 
C. F. Brush, of Cleveland, produced an arc-lamp for series street- 
lighting work which was eminently successful. The first Brush 
arc-lamp was installed in Cleveland in 1879. The first arc-lamps 
to be operated by a central lighting station were placed in the 
streets of San Francisco that same year. The Wanamaker 
store in Philadelphia was the first to use the new electric lamp 
in America, 

256 




THE FIRST ELECTRIC-LIGHT STATION IN THE WORLD, APPLETON, WISCONSIN 



APPENDIX 

William Wallace, of Ansonia, Connecticut, and Prof. Moses G. 
Farmer, of Salem, Massachusetts, exhibited a dynamo for arc- 
lighting service at the Philadelphia Centennial in 1876. But the 
lighting of city streets with electricity really began in 1881. 
Since then arc-lamps have been improved upon until those of 
to-day are vastly more efficient and give a better light than those 
first designed. 

The Search for the Incandescent Lamp 

They say that Sir William Grove made a small electric lamp 
out of platinum wire in 1840. If so, it was soon forgotten. Five 
years later John W. Starr, of Cincinnati, made one of the first 
incandescent lamps, using a bit of carbon in a vacuum globe. 
Starr died very young, on his return from England, where he went 
to take out patents for his new lamp, before he had a chance to 
perfect his work. It was demonstrated by Starr, however, that 
a small electric lamp could be made from a bit of carbon inclosed 
in a vacuum globe. Even after he had blazed the way the new 
lamp was long in coming. Inventors in Europe and America 
worked night and day to discover the proper carbon for this lamp 
filament. Wonders were thought to have been accomplished 
when a lamp was made having a life of ten hours. All of these 
first lamps were crude and cumbersome. They had to be made so 
the carbon rod could be replaced, and the air exhausted after each 
replacement. The prize was won by Thomas A. Edison in 1879. 
Edison sent his agents all over the world looking for plants and 
wood fiber which could be carbonized for the new lamp. In far- 
away Japan he found a specie of bamboo which made the new 
lamp possible. Bamboo fiber was used until 1894, when a proc- 
ess for making artificial carbon was discovered. The new proc- 
ess consisted of squirting vegetable cellulose through a die, as 
a spider spins her web. This thread was carbonized in an electric 
furnace and made into lamp filaments. The cellulose filament 
enjoyed its brief day until it was superseded by the rare metal 
tantalum in 1906. The tantalum lamp was a really great inven- 
tion, using but half the current of the carbon lamp, but its glory 
was of the briefest. No sooner was the new tantalum incandes- 
cent lamp placed on the market than a better lamp was discovered. 

259 



HARPER'S BEGINNING ELECTRICITY 

A German had worked the rare metal tungsten into lamp filaments 
and found it to be twice as economical as tantalum and three 
times better than the old carbon lamp. 

World's First Electric-Light Station 

The very first electric-light station was at Appleton, Wisconsin. ■ 
This was but a plain, wooden building just large enough to house ! 
a water-wheel-driven generator. j 

Thomas A. Edison opened the first large electrical supply i 
station for the distribution of electricity in New York City in ! 
1 88 1. He had to invent a cable which could be laid beneath the I 
streets without losing its conductivity by contact with the earth 
and moisture. He had to invent electric meters to tell how much 
electricity his customers were using for their lights. He had to' 
devise lamps, fittings, shades, etc. He proved that electricity 
could be carried from house to house on small wires, and sold in 
any quantity needed. Since that date, only a few years ago, 
nearly every city and large village in this country has installed, 
electricity for light, heat, and power. I 

The storage battery for storing electricity was invented in 18591 
by G. Plante. It was improved in 1881. This battery is still in 
service wherever it is desirable to store electricity for future use. i 

! 
The Beginning of the Telephone j 

■1 
In 1876 two men walked into the Patent Ofiice at Washingtoni 
within two hours of each other and applied for a patent on anj 
electric telephone. Alexander Graham Bell filed his papers first, | 
and to him is given the credit for the telephone, although Elishaj 
Gray was working along the same fines and escaped being famous 
by only two hours. Edison and others added many improvements 
to Bell's telephone. At first the telephone was thought to be but 
a toy, and Bell had the hardest kind of work getting the businessj 
men to indorse it. 

Dating from Davenport's toy electric railway it was forty-two 
years before the first actual electric railway was built. After the 
rediscovery of the electric motor in 1873 motors were built in' 
large sizes, and experiments were made to haul trains by motor- 

260 




INTERIOR CHICAGO ELECTRIC-LIGHT PLANT TWENTY-FIVE YEARS AGO 




INTERIOR CHICAGO ELECTRIC-LIGHT PLANT TO-DAY 



APPENDIX 

power. Thomas A. Edison, Frank J. Sprague, S. D. Field, C. J. 
Van Depoele, and others experimented in electric traction. Dr. 
Werner Siemens in 1879 built and operated a successful electric 
railroad in Berlin. This road was but a thousand feet long, and 
the passengers rode just for the novelty of it. Three years later 
Edison, at Menlo Park, New Jersey, was carrying passengers on 
his experimental train hauled by an electric locomotive. But 
the first commercial street-railway to be operated by electricity 
was the product of the genius of Frank J. Sprague, a midshipman 
in the United States navy. The road was opened in the city of 
Richmond, Virginia, in 1885. 

The transmission of electricity was taken up by Lucian Gau- 
lard in 1883. He produced the transformer, a device for raising 
the voltage, or pressure, of the electric current. Gaulard showed 
that electricity, under high pressure, could be transmitted over 
long distances without serious loss. 

The first crude dynamos, motors, transformers, arc-lamps, 
instruments, etc., which astonished the world when electricity 
sprang into importance less than twenty-five years ago, are now 
relics carefully guarded in museums. While they employed many 
of the principles still in use, they hardly resemble their successors 
of to-day. They served to open the way for future development, 
and the progress of electricity during the past few years has been 
too rapid to be recorded in anything but large volumes. 

Transmitting the New Energy 

In 1880 alternating current was distributed at 2,000 volts. Ten 
years later the first long transmission line was built at Telluride, 
Colorado, transmitting alternating current at 3,000 volts for several 
miles. This was thought a wonderful achievement. Electricity 
is transmitted to-day for hundreds of miles at potentials far above 
100,000 volts. 

The X-rays were discovered by W. C. Roentgen, of Munich, in 
1895. This was the year when many large water-power develop- 
ments w^ere started. These water-powers were formerly of little 
value ow^ng to the fact that they were so far away from shipping 
centers. When it was discovered that the water-powers could be 
changed into electrical energy and transmitted to the cities they 
16 263 



HARPER'S BEGINNING ELECTRICITY 

w 

became valuable. In 1900 a 25,cxx>volt transmission line was 
run from the Apple River, in Wisconsin, to St. Paul. Very re- 
cently the great Mississippi was harnessed at Keokuk, Iowa, and 
its thousands of horse-power in electrical energy are being dis- 
tributed to cities and towns within a radius of two hundred miles. 

A fews years ago Marconi, a school-boy, startled the world with 
his wireless-telegraph system. The fact that electrical waves will 
readily travel through the air was demonstrated b}^ Hertz long 
before this, but Marconi made use of these waves in the sending 
and receiving of messages. Since then the wireless telegraph has 
been developed until messages can readily be exchanged over 
thousands of miles. In 1906 the New York City terminal of the 
New York Central and Hudson River Railroad was electrified. 
This was the first large installation of electric locomotives, although 
they had previously been used by the Baltimore and Ohio 
and other roads. 

In 1905 an electric generator of five thousand horse-power, 
driven by a turbine steam-engine, was announced as the largest 
in the world. To-day that engine stands in the city of Schenectady, 
New York, as a monument to electrical progress, being already 
out of date and replaced with a 30,000-horse-power turbo-gen- 
erator. 

Every year sees many improvements and new inventions in 
electricity. Scientists already predict that when our coal supply 
is gone the world will have to depend upon electricity. Then we 
will have to harness all the rivers and larger streams to produce 
electricity for light, heat, and power. 




NEW MODEL ELECTRIC LOCOMOTIVE FOR NEW 
YORK CENTRAL AND HUDSON RIVER RAILROAD 




ELECTRIC LOCOMOTIVE EXHIBITED AT WORLd's FAIR IN 1893 



THE ELECTRICAL DICTIONARY 



Electrical Terms Explained 



A. C. Abbreviation for alter- 
nating current. 

Accumulator. A secondary or 
storage battery. A condenser, such 
as the Ley den jar. 

Aerial. The elevated wire an- 
tenna of a wireless system. Used 
to send and receive the electrical 
waves which pass through the air. 

Air-gap. The air-space between 
circuit terminals over which the cur- 
rent arcs. The distance between 
conductors. 

Alloy. A metal formed by melt- 
ing and mixing two or more differ- 
ent metals. Bronze is an alloy of tin 
and copper. Brass is an alloy of 
copper and zinc. 

Alternating Current. An elec- 
tric current which reverses its direc- 
tion of flow over the circuit many 
times a second. A current which 
reverses itself sixty times a second is 
said to be a sixty-cycle circuit. 

Alternator. An electrical gener- 
ator, or dynamo, which produces an 
alternating current. In large alter- 
nating-current generators the field 
revolves and the armature stands 
still. 

Amalgam. An alloy of mercury 
and silver, or mercury and zinc, etc. 

Ammeter. An instrument for 
measuring the amperes, or rate of 
flow, of an electric current. 

Ampere. After Andre Marie Am- 
pere, the French physicist, who dis- 
covered electromagnetism. The prac- 



tical unit of electric current indicating 
quantity — not pressure. One am- 
pere is the amount of current which 
will pass through a resistance of one 
ohm under a potential of one volt. 

Anode. The positive terminal of 
a battery. Opposed to cathode. 

Antenna. The elevated wires 
used to send and to receive a wireless 
message. 

Arc. In the shape of an arch. 
The brilliant bow of light which ap- 
pears between the terminals of an 
electric circuit when the current 
leaps an air-gap. 

Arc-lamp. A lamp in which the 
electric arc is used as a source of 
light. There are several kinds of 
arc-lamps. All depend upon the 
arcing of the electric current across 
an air-gap as the source of light. 
The common arc-lamp consists of 
two carbon rods separated for a 
short distance. In leaping this air- 
gap the current heats the tips of the 
rods white-hot. 

Armature. The soft-iron "keep- 
er" which is placed across the poles 
of a magnet to preserve the mag- 
netism. The vibrating disk in a 
telephone. The movable part of an 
electromagnetic apparatus. That 
part of an electric dynamo carrying 
the conductor wires which are rotated 
in the magnetic field. That part of 
the electric motor which produces 
mechanical power. 

Armature Coils. The coils of 
wire in an armature which cut the 
lines of force in the magnetic field. 



Z^i"] 



HARPER'S BEGINNING ELECTRICITY 



Armature Core. The soft-iron 
core which carries the rotating coils 
in an electric generator or motor. 

Aurora. A luminous display in 
the sky about the poles of the earth. 
Caused by electrical disturbance. 

B 

Batteries. Generators of electri- 
cal energy by chemical action. The 
primary battery produces a steady 
flow of current from the action of a 
chemical on the battery plates. The 
secondary batterv^ stores up electrical 
energy in the form of chemical energy*. 

Bi-polar. Having two poles. 

Brushes. The electrical conduc- 
tors which transmit current to or 
from the revolving parts of a motor 
or dynamo. Brushes are usually 
made of brass or sticks of carbon. 

B. T. U. British thermal unit. 
The unit for measuring heat. The 
amount of work required to heat one 
pound of water one degree. 

Buzzer. An electromagnetic alarm 
which produces a buzzing noise when- 
ever the current is flowing. Used in 
signaling, for burglar-alarms, etc. 



Cable. An insulated, armored'wire 
or wires used to transmit electrical 
currents. Generally employed for 
protecting imdergroimd and sub- 
marine wires. 

Candle-power. One candle-power 
is the Hght given by an ordinary 
candle. The unit for measuring 
illumination. A sixteen-candle-power 
lamp will give the Hght of sixteen 
ordinary candles. 

Carbon. A non-metallic electri- 
cal conductor used in electrical work. 
Charcoal, coke, and lampblack are 
almost pure carbon. It is used for 
the inactive element in batteries, in 
place of copper, in arc-lamps, in in- 
candescent lamps of the old type, 
for the brushes of dynamos and 
motors, and for telephone receivers. 

Cathode. The negative electrode 
in a batteiy. Opposed to anode. 



Cell. The unit of a batter\-. A 
battery cell consists of two plates, 
or electrodes, an anode and a cath- 
ode plate immersed in an acid solu- 
tion. 

Centigrade. A thermometer used 
for measuring temperatures in which 
the melting-point of ice is taken as 
zero. 

Charge. The quantity of elec- 
tricity present on the stirface of a 
body or conductor. A wire is said 
to be "charged" when it is carrjring 
a current of electricity. 

Circuit. A complete conducting 
path for an electric current. 

Circuit-breaker. A device to 
open and close the circuit. 

Circuit, short. An accidental 
connection through which the current 
flows, deserting its proper course. A 
circuit of low resistance. 

Code. The dots and dashes used 
to represent letters in telegraphing 
or signaHng. The system of dots and 
dashes worked out by jMorse, the 
inventor of the telegraph, is most 
extensively used. 

Collector-rings. The copper rings 
on an alternating - current dynamo 
or motor which are connected to the 
armature wires and over which the 
brushes sHde. 

Commutator. A mechanical de- 
vice for changing the direction of an 
electric current. The revolving part 
of a direct-current dynamo or motor 
which makes a sHding contact with 
the brushes. The parts of the com- 
mutator are connected to the arma- 
ture coils. 

Condenser. An apparatus for 
acctmiulating or condensing elec- 
tricity. Generally used in connec- 
tion with static generators, induction- 
coils, wireless telegraphy, etc. 

Conductors. Any material 
through which electricity will flow. 
All the metals, the earth, most chemi- 
cal solutions, and a number of non- 
metaUic substances, such as carbon, 
are all good conductors. Glass, mica, 
rubber, etc., are not conductors. 

Core. The soft-iron, central part 
' of an electromagnet or armature. 

268 



THE ELECTRICAL DICTIONARY 



Coulomb. The unit representing 
the quantity of current. The amount 
of current conveyed by one ampere 
in one second of time. 

Current. The flow of electricity. 
Corresponding to the flow of a stream 
of water. 

Cycle. The complete single ac- 
tion, or impulse, of an alternating 
current. From the generator through 
the circuit to the left and from the 
generator through the circuit to the 
right constitutes a cycle. 



D. C. Abbreviation for direct 
current. 

Detector. A magnetic device for 
detecting the presence of weak elec- 
tric currents. 

Dielectric. A non-conductor of 
electricity. 

Direct Current. An electric cur- 
rent which flows continuously in one 
direction. Opposed to alternating 
current. 

Discharge. The equalization of 
potential difference. Example : light- 
ning discharge. 

Dry Battery. A form of open- 
circuit chemical battery in which 
the solutions are in paste form. 

Dynamic Electricity. Electricity 
in motion. Opposed to static elec- 
tricity. 

Dynamo. A machine to produce, 
or generate, electricity by mechanical 
power acting on magnets. In the 
electrical industry the word dynamo 
is no longer used, generator being 
more appropriate. 



Electrode. The poles of a battery 
— anode and cathode. The carbon- 
rod terminals in an arc-lamp. 

Electrolysis. Chemical decom- 
position caused by an electric current. 
The separation of a chemical com- 
pound into its elements. 

Electrolyte. The chemical solu- 
tion in a battery. 



Electromagnet. A soft-iron core 

surrounded by a coil of insulated 
wire, which becomes a magnet only 
while electric current is flowing 
through the wire. 

Electromotive Force. Usually 
abbreviated E. M. F. The force 
which causes a current to flow over a 
conducting circuit. 

Electrophorus. A device invented 
by Volta for producing static elec- 
tricity by induction. 

Electroplating. To coat, or plate, 
with metal by the passage of an elec- 
tric current through a chemical 
solution. 

Electroscope. An instrument for 
detecting the presence of an electric 
charge. 

E. M. F. The abbreviation for 
electromotive force. The force which 
causes a current to flow. 



Faradic Currents. Currents pro- 
duced by the induction-coil, etc. 

Field. The region of magnetic 
influence surrounding the poles of a 
magnet. 

Field-magnet. That part of a 
dynamo or motor whose magnetism 
is continuous. It is always station- 
ary in direct-current machines, but 
may be either stationary or revolving 
in alternating-current generators. 

Filament. That part of an in- 
candescent lamp which emits light. 
It is a piece of fine wire of high re- 
sistance, looped many times, which 
is made white-hot by the passage 
of an electric current. 

Frequency. The number of times 
an electric current changes its direc- 
tion of flow. It is usually expressed 
in cycles per second. 

Friction. Resistance to motion. 

Fuse. A short conductor of high 
resistance and low melting-point, 
which melts and breaks the circuit 
in case the current becomes stronger 
than desired, thus protecting the 
apparatus in the circuit from damage. 
A fuse is a protector, and when it 
blows out it is merely doing its duty. 



269 



HARPER'S BEGINNING ELECTRICITY 



Galvanic Cell. A battery to pro- 
duce electricity by chemical action, 
so called after Galvani, an Italian 
scientist, who discovered the battery. 

Galvanometer. A delicate in- 
strument used to detect and to 
measure current strength, 

Galvanoscope. An instrument 
used to detect the presence of static 
electricity. 

Generator. Any apparatus capa- 
ble of producing electricity. Usual- 
ly applied to machines operated by 
mechanical power. A dynamo. 

Ground. The earth when used 
as an electrical conductor. Any 
electrical connection with the earth. 
A defect in the circuit through which 
the current escapes to the earth. 



H 



Helix. A spiral coil of insulated 
wire. 

Horse-power. The unit of me- 
chanical power. It is the energy re- 
quired to raise 33,000 poimds one 
foot in one minute. An electrical 
horse-power is equal to 746 watts, 
or approximately three-quarters of 
a kilowatt. 



Incandescent Lamp. An electric 
light in which a filament of high 
resistance is inclosed in a vacuum 
globe and heated white-hot by the 
passage of an electric current. 

Induction. The influence exert- 
ed through space by a magnet or a 
current-carrying wire. 

Insulator. Any material which 
will not readily conduct electricity. 
A substance whose resistance is so 
high that no current can pass. Glass, 
dry wood, rubber, silk, wax, shellac, 
etc., are good insulators. 

Interrupter. A device to "make" 
and "break" a circuit. 



Joule. The unit for measuring 
heat. The amount of heat generated 



by one ampere flowing for one second 
through a resistance of one ohm. 

K 

Kilowatt. A kilowatt is a thou- 
sand watts. It is used as a basis 
for figuring light and power bills too 
avoid large figures. Electrical energy 
is sold by the kilowatt-hour, or the 
use of one kilowatt for one hour. 



Leyden Jar. A form of con- 
denser for storing electricity. 

Lightning - arrester. A device 

which will permit high-voltage cur- 
rent to escape to earth, but which 
will not allow the low voltage of the 
line to escape. 

Line. Often used in place of the 
word circuit, and meaning the same. 

Load. The amount of work being 
done by a generator or motor. When 
a generator, or motor, is working at 
maximum it is said to be carrying a 
full "load." 

Lodestone. A natural magnet 
composed of iron ore impregnated 
with carbon. 

M 

Magnet. A material polarized by 
electricity and capable of magnetic 
influence. 

Magnet Coils. The insulated 
coils of an electromagnet. 

Magneto-generator. A small 
djmamo, or generator, in which per- 
manent magnets are used for the 
field. Extensively used for gaso- 
lene-engine ignition. 

Meter. To measure. Ammeters 
are used to measure amperes. Volt- 
meters to measure volts, and watt- 
meters to measure watts, etc. 

Molecule. The smallest part of 
any substance. Supposed to be 
made up of atoms of different sub- 
stances. 

Motor. A device to change elec- 
trical energy into mechanical energy 
so it can be utilized to operate railway- 
cars, machinery, etc. 



270 



THE ELECTRICAL DICTIONARY 



Motor-generator. A motor and 
a generator coupled together for 
changing alternating current to di- 
rect current, and vice versa. 

Multiple. When several pieces 
of electrical apparatus are connected 
in parallel with each other. 



N 



Negative. The negative current; 
opposed to positive. 

Neutral Wire. The central wire 
in a three-wire distribution system. 

Non-conductor. Not a conduc- 
tor. Any material which offers very 
high resistance to the passage of 
electricity. 

O 

Ohm. The unit of electrical re- 
sistance. All electrical conductors 
offer more or less resistance to the 
passage of the current, and the 
amount is expressed in ohms. The 
volts divided by the amperes will 
give the resistance of any circuit in 
ohms. If there is a potential of 24 
volts, causing a current of 4 amperes, 
the resistance will be 24 divided by 
4, or 6 ohms. 

Ozone. An oxidizing gas pro- 
duced by the passage of a high- 
potential current through the air. 



Parallel Circuits. Two conduc- 
tors laid side by side. 

Polarization. When a voltaic cell 
is prevented from producing electro- 
motive force by a non-conducting 
film of gas or chemicals. 

Pole. The terminal of a battery, or 
the magnetic end of a magnet. Bat- 
tery poles are positive and negative; 
magnet poles are north and south. 

Positive Electricity. The current 
that flows from the positive pole of 
a battery or generator. 

Potential. The pressure, or ca- 
pacity for work, of an electric cur- 
rent. It is expressed in volts. 

Primary. Opposed to secondary. 
The first coil in a transformer. 



Receiver. The instrument for 
receiving the electrical vibrations in 
a telephone. 

Rectifier. A device for changing 
an alternating current to a direct 
current. 

Relay. An electromagnetic de- 
vice generally used in telegraphy. A 
weak current acting on a relay 
operates a stronger current for long- 
distance service. 

Resistance. The quality which 
all conductors have of impeding the 
flow of the electric current through 
them to a greater or less extent. Its 
unit is the ohm. 

Rheostat. A device containing 
conductors of considerable resistance, 
used in a circuit for the purpose of 
reducing a current which is normally 
too powerful for the apparatus it is 
intended to operate. 



Saturation. A magnet is said to 
be saturated when it will take up no 
more magnetism. 

Secondary Battery. The stor- 
age battery. 

Secondary Current. The cur- 
rent induced in the secondary wind- 
ings of an induction-coil, etc. 

Series. Literally means one after 
the other; arranged in succession. 
Opposed to multiple, or parallel. 

Short Circuit. When the cir- 
cuit is suddenly shortened by the 
current escaping through the ground 
or over any other conductor. 

Shunt. A by-path in a circuit 
by which a part of the current 
branches off from the main circuit, 
returning to it at another point. A 
shunt dynamo or motor has its field- 
coil connected as a shunt to its arma- 
ture coils; that is, the field and arma- 
ture are connected in multiple. 

Solenoid. A spiral coil of insu- 
lated wire. A helix. 

Spark-gap. The air - space be- 
tween two conductors traversed by 
the electric current. 



271 



HARPER'S BEGINNING ELECTRICITY 



Static Electricity. A riigh-ix>- 
1 ::: —':jl\:. :z.z.y i::;: ; ::: insu- 



Storage Batteries. A battery 
:i:h liicfrs flTirrlcal ener^ into 
e: :u:;. ri- :r- 3:1 stores it in this 



Sv.itch. A device to open and 
d:5; £. :ir;tdt. 

Switchboard. Aboard or panel, 
ei: -r: :: - : :r stone, to hold the 
5-1 ; tS. ::. :: iments, etc., for con- 
:r:llir:g the distribution of the cur- 



Temiinal. ihe end of an open 



Thermostat. 



Transfomier 



instrument 

E £^:: elec- 

: I. ; i^nal or 

rg-uiate the 

r if iron 

; _r coil, 

-:: led to 

: r, called 

: r i^ :3 the 

T e cur- 

E i : : ndarv 



Transmission, 



Transmitter, 



ary. Used 

onlv. 
LIE r'bution 

: ingcir- 

e; -e de- 

1 rations 

1 Eii^nsmits 



Trolley Wire. i.ike overiiead wire 
for trolley-car service. Trolley: — ^the 
device for connecting the car with 
the overheai ~ire. 

Turbo-generator A generator 
witii its rota::r.c -e i.t. ::i e e:::^ 1 e r, -Ehe 



V 

Vibrator. A spring device for 
rapidly making and breaking the 
circuit. ^ 

Volt. Jz.'z u:iiT of electromotive 
force, presEEre. e: ^ EEt::::?/.. 0:ir 
volt w31 f c r E r E :e r .' EE e: T : - : 1e r e .: r ii 
a resistance ee eel e /_: e 

Voltage. 7Ei : eeeel: e: eIts 
existing in ar.v Eir :;:_:: e: genera: et 
of electric current. 

Voltmeter. An instrument for 
measuring the voltage of a circuit. 

W 

Watt. The unit of electrical 
power. It is the rate of work of 
one ampere under a potential of one 
volt- Found by multiplying volts 
and amperes together. An electrical 
horse-power equals 746 watts; it 
may be 746 volts and one ampere, 
or one volt and 746 amperes, or any 
other two factors of 746. 

Watt-hour. The unit of power 
consumed; it equals one watt ex- 
pended for one hour, and is the usual 
basis of charge on electric light and 
power bills. 

Wattmeter. An instrument for 
r:Eea; irlr :: The watt-hours of a dr- 



Waves. electric. Electrical dis- 
turbarEe ;: "EJe errer. 

Wiring. The —ires installed for 
an elee:~ - :ir;-:^T. 



X-rays. Rays of light which are 
not visible to ordinary eyes. Such 
rays travel readily through various 
opaque bodies. 



INDEX 



Accumulator, 52, 53. 

Air-gap, 18, 48. 

Alternator, 179. 

Ampere, loi, 102. 

Anode, dj. 

Arc-lamp, 215, 256; miniature, 216. 

Armature, no, 166, 167. 

Attraction and repulsion, 23, 24, 

26, 27. 
Automobile, electrical equipment, 

227. 
Automobile lamps, 229, 230, 231, 

232, 235. 

Battery, action of, 70; circuits, 
84, 85, 88; closed circuit, 71; 
current, 87, 88; defect, 69; dis- 
covery of, 247; dry, 81, 82; ex- 
periments, 75, 79, 80, 91; grav- 
ity type, 82, 83; open-circuit, 71; 
primary, 73; secondary, "jy., stor- 
age, 73, 236; wet, 68. 

Bells, electric, 129, 130. 

Brush discharge, 47. 

Buzzer, 145. 

Candle-power, 226. 

Cathode, 6"]. 

Cell, battery, dy. 

Charged, 19. 

Circuit, 7, 47, 96, 97, 98, 99, 100; 
electric as compared to water, 7, 
8; ground-return, 105; metallic, 
105; short, 97; shunt, 183, 194. 

Code, Morse, 153, 154. 

Coil, induction, 133; magnetic, 123, 
124; primary, 131, 132, 134; 
secondary, 131, 132, 134. 

Collector, 40, 44. 



Commutator, 166, 168, 182. 
Condenser for induction-coil, 138. 
Conductor, 9, 21. 
Connector, 83. 
Cooking by electricity, 205. 
Coulomb, 102. 

Current, alternating, 168, 171, 172; 
direct, 168. 

Detector, 76, 77. 

Diamagnetic, 116. 

Discharged, 19. 

Discharger, 49, 50. 

Dynamics, 165. 

Dynamo, i, 174, 175; discovery of, 

2S4> 255; experimental, 175, 176, 

177. 

Electric fish, 241. 

Electricity, dynamic, i, 165; gal- 
vanic, I, G'j; static, i, 14, 15, 16, 
20, 21. 

Electrodes, d'j. 

Electromagnet, 112, 113; discovery 
of, 250; to make, 126, 127, 128. 

Electromotive force, dj, 68, 72, 73. 

Electrophorus, 36, 37. 

Electroscope, 28, 29, 30, 31. 

E. M. F. of various batteries, 72. 

Energy explained, 11, 12; trans- 
mission of, 171. 

Field, magnetic, 167; of force, 32, 

33, 34, 112, 114, 178, 179. 
Flatiron, electric, 206. 
Fuse, 207. 



Galvanic electricity, dj'., pile, 

74> IS- 



273 



HARPER'S BEGINNING ELECTRICITY 



Galvanometer, 78. 
Geissler tubes, 62, 141, 142. 
Generator, 174, 175, 176, 177, 178, 
179, 187; how to make, 181, 182, 

183, 184. 
Gravitation, 2, 3. 
Ground, 41. 



Negative ELECTRiciri', 26. 
Non-conductors, 9. 

Ohm, 92, 253, 
Ozone, 51. 

Par.\llel conductors, 100, 104. 
Path, electric, 97. 



4 



Heat, electric, 199, 200, 201; ex 

perimental, 207, 208, 209; how Polarize, 69, iii. 

measured, 202, 205; how pro- Pole, batter}^, 70, 7 

duced, 202; relation to electricity^, 

201. 
Helix, 59. 
Horse-power, 103. 



Ignition, 227, 228, 229. 
Incandescent lamp, 218, 221, 259; 

miniature, 225. 
Induction, 33, 37, 45, 115, 131, 132, 



Poles, magnetic, 106, 107, 108, 117, 

118. 
Positive electricity, 25, 26. 
Potential, 10, 47, 70, 165, 168. 



Rays, magnetic, 114, 115, 116, 117, 

118. 
Receiver, telephone, 15 
Relay, telegraph, 144 



I 



141, 142; to make, 133, 134, 135 
136, 137, 138, 139 
Insulator, 9. 



I33> 166, 175 ; discover>^ of, i Repulsion, opposed to attraction, 
^ ^46.. ! 23, 24, 26, 27. 

induction-coil, 131; experiments, • Resistance, 9, 10, 92, 93, 94. 

' Rheostat, 197. 
Rotor, 198. 

Series conductors, 85, 99, 100, 

104. _ 
Short circuit, 97. 
Shunt circuit, 97, 183, 194. 
Solenoid, 113, 128, 129. 
Sounder, telegraph, 144, 147, 148, 

^ 149. 150- 

Spark-gap, 18, 

Static currents, how produced, 20, 
21; electricit}', 14, 15, 16, 17, 18, 
19; first experiments, 242, 244; 
generator, glass cj'linder, 38, 39, 
40; glass disk, 42, 43, 44; motor, 
58, 59; ^park, 47, 48, 49, 50. 

Stator, 198. 



Key, telegraph, 144, 146, 
Kinetic theory*, 199. 

Leyden jar, 54, 55, ^6, 140; 

covery of, 245. 
Light, electric, 210, 211, 212. 
Lightning, explained, 17. 
Light-waves, 211. 
Lines of force, 19, 32, 33, 34, 

115, 174, 178, 179. 
Locomotive, electric, 263, 265. 
Lodestones, 241. 



14: 



dis- 



114, 



Magnet, bar, 109; horseshoe, 109. 
Magnetic dip, 108; poles, 107. 
Magnetism, 106; discovery of, 240. 
Magneto, 166. 

Magnets, to make, 120, 121, 122. 
Motor, discoverv- of, 253; explained, 
189, 190, 191; toy, 192, 193, 194. 
Multiple conductors, 85, loo, 104. 



Telegraph, explained, 143, 144; in- 
struments, how to make, 146, 147, 
148; lines, 145, 151, 152. 

Telephone, 155; batteries for, 162; 
circuits, 163; explained, 157, 158, 
161; history of, 155, 260; parts, 



274 



INDEX 



158; simplest electric, 158, 159, 

160, 167. 
Transformer, 139, 188. 
Transmission, 263. 
Transmitter, telephone, 158. 



Vapor-lamp, 222. 

Vibrator, for induction-coil. 



36, 



Volt, definition of, 48, 102. 
Voltage, 10. 
Voltmeter, 103. 

Watt, definition of, 102. 

Wattmeter, 103. 

Waves, electric, 4; sound, 155, 156, 

Wiring, automobile, 232, 233, 234. 



THE END 



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